Projects to look into

I often stumble into projects that I don’t have time to look into immediately. This is a list of projects that I keep as a note to self.

Qt specific

https://api.kde.org/frameworks/kquickcharts/html/index.html
https://github.com/219-design/qt-qml-project-template-with-ci
https://github.com/ABBAPOH/learnopengl-qt Qt-ified examples from learnopengl.com
https://github.com/Ableton/aqt-stylesheets
https://github.com/ArsMasiuk/qvge Qt Visual Graph Editor, with graphviz support
https://github.com/BrigJS/brig JS-only apps using Node and Qt Qml
https://github.com/CefView/QCefView Widget encapsulating Chromium Embedded Framework (CEF)
https://github.com/ChristophHaag/motorcar 3D compositor system with QtWayland
https://github.com/CrimsonAS/gtkplatform
https://github.com/Daguerreo/QMLTreeView QML tree view with a C++ model
https://github.com/DavidXanatos/NeoScriptTools Qt6 compatible fork of Qt4 ScriptTools
https://github.com/DeiVadder/QtPhrasebookUtilityTool TS/qph/translation tools
https://github.com/Furkanzmc/QML-Coding-Guide Some opinionated "best" practices
https://github.com/Furkanzmc/QML-UI-Animations QML implementation of some mockup UIs
https://github.com/Furkanzmc/qml_widgets Use QtWidgets with QML
https://github.com/GillesDebunne/libQGLViewer Helper to make 3D views (camera, screenshot, etc)
https://github.com/HamedMasafi/QInjection Dependency injection for Qt
https://github.com/HappySeaFox/qsseditor Edit and preview style sheets
https://github.com/JackyDing/QtFlex5 Flexible and dockable widgets for Qt5
https://github.com/Megaxela/QCodeEditor Code editor widget with some features
https://github.com/MidoriYakumo/learnopengl-qt3d learnopengl.com’s examples in Qt3D
https://github.com/OlivierLDff/QOlm QAbstractListModel wrapping a list of QObject
https://github.com/OlivierLDff/Qaterial Material Components on QtQuickControls
https://github.com/QuasarApp/Qt-Secret Wrapper of OpenSSL with Qt
https://github.com/SeriousAlexej/TabToolbar Allow creating tabbed toolbars
https://github.com/Skycoder42/QtMvvm
https://github.com/Skycoder42/QtService library to easily create system services
https://github.com/Tannz0rz/GridStarLayout
https://github.com/VSRonin/QtModelUtilities
https://github.com/ableton/aqt-cassowary Use a constraint solver for layouting QML applications
https://github.com/addisonElliott/HttpServer Qt-based HTTP server
https://github.com/agateau/cookiecutter-qt-app
https://github.com/alamminsalo/qmlnotify
https://github.com/antony-jr/QArchive libarchive wrapper
https://github.com/approximator/Qt-Qbs-Application
https://github.com/apripolzin/LearnOpenGl_Qt6
https://github.com/arnt/qt-history2 Old history of the Qt repository
https://github.com/azrilrahim/qt-rfb-client RFB or VNC client 100% based on Qt
https://github.com/bwalter/qt-promise Chainable promises (unreviewed)
https://github.com/canonic/canonic Web browser that runs WASM
https://github.com/danvratil/qcoro Qt-integrated coroutine support
https://github.com/darkmattercoder/qt-build Qt build environment inside Docker
https://github.com/develtar/qt-pdf-viewer-library Renders PDF in a WebView using PDF.js
https://github.com/ec1oud/qqchart Simple line charts in Qt Quick using the GPU
https://github.com/ec1oud/qt-tuio-sender
https://github.com/emericg/QmlAppTemplate App template with deployment support
https://github.com/f35f22fan/Ods2 ODS (Open Document Spreadsheet) with Qt
https://github.com/faaxm/spix UI test automation library for QtQuick/QML
https://github.com/filcuc/dotherside C library for bindings to QML
https://github.com/forderud/QtWasm Docker container for building with Qt WASM
https://github.com/fpoussin/Qt5-MSVC-Static
https://github.com/fpoussin/QtUsb
https://github.com/githubuser0xFFFF/Qt-Advanced-Docking-System
https://github.com/githubuser0xFFFF/Qt-Advanced-Stylesheets
https://github.com/githubuser0xFFFF/QtFreeVirtualKeyboard
https://github.com/gnomezgrave/qt-auto-translator Translate TS files semi-automaticly
https://github.com/gongjianbo/EasyQPainter Several easy QPainter demos (including 3D ones)
https://github.com/gpospelov/qt-mvvm
https://github.com/guerinoni/qTsConverter Convert TS to spreadsheet
https://github.com/jcelerier/qml-creative-controls
https://github.com/jkriege2/JKQtPlotter
https://github.com/jpnurmi/qtjsongadget QObject/Q_GADGET to JSON
https://github.com/juangburgos/QDeferred alternative to async threaded execution
https://github.com/juangburgos/QUaModbusClient
https://github.com/juangburgos/QUaServer
https://github.com/juangburgos/QUaServerWidgets
https://github.com/jurplel/QtApng Support the APNG format (animated PNG)
https://github.com/laserpants/qt-material-widgets
https://github.com/lelegard/qtlinguist-installers
https://github.com/lqt5/lqt Lua bindings (use Qt from Lua)
https://github.com/martinky/qt-interactive-coding
https://github.com/martinrotter/qt-minimalistic-builds
https://github.com/mitchcurtis/logging-ini-generator
https://github.com/miurahr/aqtinstall Qt CLI installer from official packages
https://github.com/nitroshare/qmdnsengine Multicast DNS library for Qt
https://github.com/oblivioncth/Qx Lots of different extensions to Qt’s functionality
https://github.com/olegyadrov/softwarerenderer QPainter-based 3D soft renderer
https://github.com/parhamoyan/QuteChart Chart monthly aggregated data
https://github.com/paulolav/mazecompositor Qt6 fork of the maze compositor
https://github.com/pbek/qmarkdowntextedit
https://github.com/pwuertz/QtQuickPlotScene Basic components for creating plot scenes
https://github.com/randrew/phantomstyle Cross-platform QStyle for traditionalists
https://github.com/rmallah/fakemodel Generates placeholder QML models
https://github.com/simulton/QSchematic Make diagrams like flowcharts or engineering schematics
https://github.com/stereomatchingkiss/QImageScraper Image scrapper using Qt WebEngine
https://github.com/tetsurom/rxqt Qt integration with RxCpp (reactive cpp)
https://github.com/uwerat/qpagbm Platform plugin for offscreen Qt/OpenGL applications
https://github.com/uwerat/vnc-eglfs VNC server for Qt/Quick on EGLFS
https://github.com/vioken/qwlroots Bindings to wlroots (wayland compositor library)
https://github.com/vioken/waylib Wrapper for wlroots (unclear relation with qwlroots)
https://github.com/vladimir-kraus/qtutils

Note	https://github.com/itay-grudev/SingleApplication Single application with support for inter-instance communication (but careful, likely not open source since 3.4.0 and newer, use 3.3.4).

Frameless window support

This is an oddly popular subject in Github, it seems…

https://github.com/Jorgen-VikingGod/Qt-Frameless-Window-DarkStyle
https://github.com/antonypro/QGoodWindow Borderless window in Qt5/Qt6
https://github.com/qtdevs/FramelessHelper frameless window, full features
https://github.com/stdware/qwindowkit
https://github.com/wangwenx190/framelesshelper Frameless window, widgets/quick

C++ libraries/projects

https://github.com/AnthonyCalandra/modern-cpp-features a sort of cheatsheet
https://github.com/ArthurSonzogni/FTXUI Library for terminal user interfaces
https://github.com/BowenFu/matchit.cpp Pattern matching, header only
https://github.com/David-Haim/concurrencpp Support for tasks, executors and coroutines
https://github.com/HO-COOH/SugarPP Some syntax sugar facilities
https://github.com/KonanM/tser Very tiny serialization library
https://github.com/Naios/idle asynchronous and hot-reloadable C++ framework
https://github.com/Neargye/magic_enum Like QEnum, but with different pros/cons
https://github.com/Neargye/nameof obtain the name of a variable, type…
https://github.com/SpartanJ/efsw Cross platform filesystem watching
https://github.com/TartanLlama/generator Generator for coroutines, ranges support
https://github.com/ThePhD/infoware Library for pulling system/hardware information
https://github.com/UltraEngine/tableplusplus C++ library for tables that behave like Lua’s
https://github.com/Viladoman/StructLayout Visualize layout of C++ structs
https://github.com/VincentZalzal/noisy Header that prints calls to every special member function
https://github.com/akrzemi1/explicit Utilities like tagged_bool and not_null
https://github.com/aras-p/ClangBuildAnalyzer build analysis using -ftime-trace
https://github.com/atomgalaxy/libciabatta Mixin library
https://github.com/bkryza/clang-uml UML diagram generation from C++ sources
https://github.com/bloomen/transwarp Task concurrency via a graph of tasks
https://github.com/boost-ext/mp Make meta-programming the same as runtime programming
https://github.com/camio/modules-example Simple Makefile/clang-based example of C++ modules
https://github.com/changkun/modern-cpp-tutorial Large book-like tutorial
https://github.com/cieslarmichal/faker-cxx Library for generating fake data of many kinds
https://github.com/cpp-testing/GUnit Simplifies and improves GMock and GTest
https://github.com/cppfastio/fast_io Fast input/output library
https://github.com/danielaparker/jsoncons JSON, CBOR, MessagePack, etc
https://github.com/davidstone/bounded-integer library for bounded integers
https://github.com/duneroadrunner/scpptool Project to attempt to provide a "safer" C++ subset
https://github.com/e-fever/xbacktrace
https://github.com/edubart/minilua Lua packed into a single header
https://github.com/effolkronium/random Very simple to use function to generate random numbers
https://github.com/emil-e/rapidcheck Property based testing in C++
https://github.com/eyalz800/zpp_bits Serialization and RPC (unobtrusive)
https://github.com/eyalz800/zpp_throwing Coroutines as exceptions alternative
https://github.com/google/highway Performance-portable, length-agnostic SIMD with runtime dispatch
https://github.com/google/integers Safe integers (custom behavior)
https://github.com/googleprojectzero/weggli semantic search tool for C and C++
https://github.com/grandseiken/static-functional Compile-time functional wrappers
https://github.com/jart/cosmopolitan build-once run-anywhere C and C++ library
https://github.com/jeremy-rifkin/floating-pointers Pointers on floating point numbers (humor)
https://github.com/jeremy-rifkin/libassert Fancy assertion library
https://github.com/jimmiebergmann/mini-yaml Header-only YAML library
https://github.com/jmarkowski/codeviz Generates a graphviz graph of header dependencies
https://github.com/joboccara/NamedType
https://github.com/johnmcfarlane/unformat generates .clang_format from code
https://github.com/lamarrr/STX C++ 20 error-handling and utility extensions
https://github.com/lucasg/Dependencies A rewrite of the old legacy software "depends.exe"
https://github.com/marzer/poxy Doxygen-based documentation generator in Python
https://github.com/mgehre/xunused Find unused code across source files
https://github.com/microsoft/mimalloc Compact, fast general purpose allocator
https://github.com/mpark/patterns Pattern matching for C++17, evolved to P1371
https://github.com/mstorsjo/llvm-mingw LLVM/Clang/LLD based mingw-w64 toolchain
https://github.com/mutouyun/cpp-ipc IPC library for Linux/Windows via shared memory
https://github.com/ned14/outcome
https://github.com/nemequ/pre-defined-macros List of compiler provided defaults
https://github.com/nholthaus/statistics Calculate statistics on a set of data
https://github.com/nucleic/kiwi Efficient Cassowary constraint solver (e.g. for layouts)
https://github.com/onqtam/doctest Test/assertion library, small footprint
https://github.com/open-license-manager/licensecc Library and utilities for licensing software
https://github.com/p-ranav/alpaca Serialization library
https://github.com/p-ranav/tabulate Create very pretty tables in the console
https://github.com/pfultz2/ZLang A plugin framework for namespacing macros
https://github.com/ra1u/tubez Efficient C++ library for streams
https://github.com/rollbear/strong_type An additive strong typedef library
https://github.com/rui314/mold Next gen linker by the LLD author
https://github.com/sandsmark/unfuckify Remove auto from C++ sources
https://github.com/scylladb/seastar Server side application framework
https://github.com/sheredom/utf8.h Header-only UTF-8 C/C++ lib
https://github.com/skypjack/uvw libuv wrapper in modern C++
https://github.com/tbfleming/cib clang running in browser (wasm)
https://github.com/teslamotors/fixed-containers C++20 header-only with some nice containers and helpers (e.g. enums)
https://github.com/tringi/adaptive-rounding Human-intuitive rounding of floating point numbers
https://github.com/tyckesak/laugh Simple actor concurrency framework
https://github.com/uni-algo/uni-algo Simple Unicode library
https://github.com/waitingtocompile/spool header only job-based parallelism framework
https://github.com/yse/easy_profiler C++ profiling library with Qt UI
https://ultralig.ht/ For lightly embedding an HTML UI in C++ (proprietary)
https://www.behaviortree.dev/ Library to create behavior trees

Runtime polymorphism libraries

A post on Reddit with some discussion, introduction to the ideas, and links to libraries.

http://stlab.adobe.com/grouppolyrelated.html Adobe.Poly
https://github.com/boost-ext/te Boost TE ("unnoficial boost project")
https://github.com/facebook/folly/blob/master/folly/docs/Poly.md Folly.Poly
https://github.com/iboB/dynamix (not looking great yet: macros, no documentation, etc.)
https://github.com/jamboree/polytail
https://github.com/kelbon/AnyAny
https://github.com/ldionne/dyno
https://github.com/microsoft/proxy Implementation submitted for standarization
https://github.com/skypjack/entt/wiki/Crash-Course:-poly Poly, as part of EnTT
https://github.com/stephenberry/glaze/blob/main/include/glaze/util/poly.hpp
https://www.boost.org/doc/libs/1_66_0/doc/html/boost_typeerasure.html Boost.TypeErasure

Signal/slot/property related

https://github.com/KDAB/KDBindings Bindings/signals/slots without Qt dependency
https://github.com/bitsbakery/callme header-only C++20 library of fast delegates and events
https://github.com/kevin--/bindey Object properties and data binding
https://github.com/skypjack/entt Contains a standalone delegate/signal "module"
https://github.com/wqking/eventpp Callbacks, event dispatching/queue

C++ standard-related libraries

This libraries relate to the C++ standard in one way or another. There might be alternatives to the standard types (which maybe are available in earlier compilers) or have different features, or have been proposed for standarization.

https://github.com/HowardHinnant/date Date/time library based on chrono
https://github.com/KaisenAmin/c_std C++ standard library implemented… in C
https://github.com/MKlimenko/embed Simulates std::embed support with C++17
https://github.com/RishabhRD/expected
https://github.com/Sedeniono/tiny-optional Compact optional (with extras like optional<int, -1>)
https://github.com/TartanLlama/expected C++11/14/17 with functional extensions
https://github.com/TartanLlama/function_ref Lightweight non-owning reference to a callable
https://github.com/TartanLlama/optional
https://github.com/bitwizeshift/result Inspired by std::expected
https://github.com/eliaskosunen/scnlib Text parsing proposal ("modern scanf")
https://github.com/gulrak/filesystem header-only std::filesystem compatible library
https://github.com/jbcoe/indirect_value Perfect PIMPL
https://github.com/jbcoe/polymorphic_value Polymorphic value-type
https://github.com/martinmoene/expected-lite header-only, C++11
https://github.com/mpark/variant Implementation based on Clang’s (C++ >=11)
https://github.com/vittorioromeo/scelta Improves variant/optional visitation

Units libraries

https://github.com/LLNL/units
https://github.com/aurora-opensource/au C++14, no dependencies and optionally header-only
https://github.com/mpusz/units C++ 20 library proposed for standarization
https://github.com/nholthaus/units

C++ reflection-related

https://github.com/FireFlyForLife/NeatReflection Based on C++20 module files (IFC)
https://github.com/TheNitesWhoSay/RareCpp Macro-based simple C++ reflection
https://github.com/apolukhin/pfr_non_boost Boost.PFR without the boost namespaces
https://github.com/billyquith/ponder C++ reflection with Lua binding
https://github.com/boost-ext/reflect C++20 static reflection library
https://github.com/boostorg/describe Macros for describing enumerators and struct members
https://github.com/boostorg/pfr Tuple-like methods for user defined types
https://github.com/cbeck88/visit_struct Easily reflect with intrusive and non-intrusive options
https://github.com/celtera/avendish
https://github.com/felixguendling/cista Serialization and reflection library
https://github.com/getml/reflect-cpp (de)serialization and validation using compile-time reflection
https://github.com/lock3/meta Clang fork with reflection/metaprogramming
https://github.com/rttrorg/rttr C++ reflection library
https://github.com/veselink1/refl-cpp Static reflection: compile-time enumeration, attributes, …
https://www.circle-lang.org/ Compiler with special meta-generation

Multimethods

https://github.com/dutor/loki/blob/master/Reference/MultiMethods.h
https://github.com/hutorny/multimethods Chepurni multimethods for modern C++
https://github.com/jll63/yomm2 Fast, orthogonal, open multi-methods in C++ 17
https://github.com/wickedmic/multidispatch-lib Header-only C++ 14

Entity Component Systems

Libraries in the underscore/lodash/Enumerable style for C++

Unicode or text related

https://github.com/anyascii/anyascii
https://github.com/sg16-unicode/sg16 Unicode study group
https://github.com/soasis/text AKA ztd.text
https://github.com/tzlaine/text AKA Boost.Text (but not part of Boost)

Parsers

https://github.com/foonathan/lexy Parser DSL in pure C++
https://github.com/peter-winter/ctpg Compile-time LR1 parser with pure C++ API
https://github.com/taocpp/PEGTL Parsing Expression Grammar Template Library
https://github.com/yhirose/cpp-peglib Header-only PEG library with a playground to test

Bitfield

https://github.com/SanyaNya/advanced-bitfield
https://github.com/GabrielDosReis/bits/blob/main/src/bits.ixx Bit manipulation, mostly with enums

Logging

https://github.com/muflihun/easyloggingpp Header only C++ logging library
https://github.com/PlatformLab/NanoLog Unmaintained, but part of an interesting research project

Dependency injection

https://github.com/google/fruit dependency injection framework for C++
https://github.com/gracicot/kangaru Dependency injection container
https://github.com/qlibs/di C++ 20, with plenty of compile-time functionality
https://github.com/ybainier/Hypodermic Header-only IoC containerj

Networking or adjacent

https://github.com/banach-space/clang-tutor Clang plugins for teaching and learning
https://github.com/yhirose/cpp-httplib Single header HTTP(S) client and server library
https://github.com/CrowCpp/Crow Framework for HTTP/WebSocket services
https://github.com/libcpr/cpr Developer-friendly wrapper around libcurl

Non-Qt GUI projects

https://github.com/cycfi/elements C++ GUI library with some "anti Qt" vibes
https://github.com/lvgl/lvgl MCU graphics library for making UIs
https://github.com/mikke89/RmlUi HTML/CSS User Interface library evolved
https://github.com/texus/TGUI C++ library with SDL, SFML and GLFW backends

Functional programming

https://github.com/graninas/cpp_functional_programming

Cross compilation, deployment, packaging

https://github.com/QuasarApp/CQtDeployer linuxdeployqt/windeployqt alternative
https://github.com/alex-spataru/QtApp-Template Deployment examples included
https://github.com/intoli/exodus Relocate ELF binaries
https://github.com/madduci/docker-msvc-cpp Cross compile with MSVC via Docker
https://github.com/mas-cli/mas Mac App Store command line interface
https://github.com/multiarch/crossbuild
https://github.com/mxe/mxe
https://github.com/nektos/act Run Github Actions locally
https://github.com/niXman/mingw-builds-binaries Up to date MinGW binary packages
https://github.com/paleozogt/MSVCDocker MSVC via Wine in Docker
https://github.com/saidinesh5/mxedeployqt
https://github.com/sickcodes/Docker-OSX Run macOS VM in a Docker
https://github.com/tpoechtrager/osxcross
https://github.com/wheybags/glibc_version_header Use symbols of old glibcs
https://github.com/zhlynn/zsign Codesign alternative to iOS (cross platform)

AppImage specific

https://github.com/AppImage/awesome-appimage
https://github.com/TheAssassin/AppImageLauncher
https://github.com/TheAssassin/appimagecraft
https://github.com/azubieta/appimage-firstrun Integrate app on the sytem via a first-launch dialog
https://github.com/linuxdeploy/linuxdeploy
https://github.com/srevinsaju/zap AppImage package manager

Graphics

https://alicevision.org/ Photogrammetric Computer Vision Framework
https://github.com/DadSchoorse/vkBasalt vulkan post processing layer for linux
https://github.com/a-e-k/canvas_ity Small header-only library for canvas-like API, draws to a buffer
https://github.com/alicevision/QtAliceVision Qt integration into AliceVision
https://github.com/baldurk/renderdoc Frame-capture based graphics debugger
https://github.com/bkaradzic/bgfx "Bring Your Own Framework"-style rendering library
https://github.com/chengyin/albumcolors Makes a 3 color palette to blend with an image
https://github.com/crosire/reshade post-processing injector for games and video software
https://github.com/dashandslash/QQuickBgfx Qt integration with BGFX
https://github.com/doitsujin/dxvk Vulkan-based Direct3D for Linux/Wine
https://github.com/houmain/gpupad A shader IDE-like application
https://github.com/styluslabs/nanovgXC Vector graphics library in OpenGL
https://github.com/woltapp/blurhash Very compact blurry representation of an image, as a hash
https://github.com/yuki-koyama/tinycolormap Use a colorscale to map 0→1 to a color

Unique icon generation from text

Chart-related

https://github.com/ManimCommunity/manim Mathematical animations into videos
https://github.com/ambrosiogabe/MathAnimation Video editor, like manim, but realtime
https://github.com/epezent/implot
https://github.com/thclark/cpplot

Text handling, rendering, Unicode…

https://github.com/Wisdom/Awesome-Unicode
https://github.com/janlelis/unibits
https://github.com/janlelis/uniscribe
https://github.com/r12a/uniview
https://github.com/unicode-org/cldr Common Locale Data Repository
https://github.com/unicode-org/icu4x
https://github.com/unicode-org/text-rendering-tests test suite for rendering engines

Artificial Intelligence

https://github.com/Significant-Gravitas/Auto-GPT Tool to help GPT in having memory and "templates"
https://github.com/ggerganov/llama.cpp Port of Facebook’s LLaMA model in C/C++
https://github.com/ggerganov/whisper.cpp Port of OpenAI’s Whisper model in C/C++
https://github.com/nomic-ai/gpt4all ecosystem of open-source chatbots
https://github.com/imartinez/privateGPT Interact privately with your documents

Development in general

https://bellard.org/jslinux/ Run Linux on the browser
https://bellard.org/quickjs/ JavaScript implementation
https://github.com/CoatiSoftware/Sourcetrail Source explorer to learn new code bases
https://github.com/H-M-H/Weylus tablet as graphic tablet/touch screen on your computer
https://github.com/Theldus/PBD Debugger which prints variable values instead
https://github.com/c-smile/sciter-sdk UI C++ framework for HTML/JS (not OSS!)
https://github.com/dev-0x7C6/fdt-viewer Qt-based GUI viewer for Device Trees
https://github.com/epasveer/seer Qt-based GDB frontend
https://github.com/eteran/edb-debugger Qt-based debugger for RE
https://github.com/flamegraph-rs/flamegraph Easy flamegraph generation for perf
https://github.com/google/bloaty Size profiler for binaries
https://github.com/google/orbit C/C++ performance profiler
https://github.com/google/wuffs Language to parse untrusted file formats
https://github.com/haampie/libtree ldd substitute with many more features
https://github.com/jart/blink Tiny cross-platform (via cosmopolitan) x86-64-linux emulator
https://github.com/jart/cosmopolitan Actually Portable Executable: multi-os binaries
https://github.com/jart/cosmopolitan/releases/tag/pledge-1.8 sandboxing CLI commands on Linux
https://github.com/lowlighter/metrics infographics about your GitHub account
https://github.com/mozilla/sccache ccache with cloud storage, icecc capabilities
https://github.com/nothings/stb Miscellaneous super-minimal libraries
https://github.com/paritytech/cachepot sccache fork "with better security"
https://github.com/shopify/toxiproxy Make the network fail on purpose
https://github.com/sidkshatriya/rd RR (record and replay) rewritten in Rust
https://github.com/spack/spack Package manager supporting multiple versions
https://github.com/webview/webview Tiny webview integrating native engine

Text validation, templating, or programmatic configuration generation

Summary and other links: https://github.com/oilshell/oil/wiki/Survey-of-Config-Languages

https://cuelang.org/ Validate, define, and use dynamic and text-based data
https://dhall-lang.org/ A programmable configuration language
https://jsonnet.org/ A data templating language for app and tool developers
https://nestedtext.org, https://github.com/KenKundert/nestedtext Human Friendly Data Format

Lua

https://github.com/1bardesign/batteries Reusable dependencies for Lua (specially LÖVE) games
https://github.com/airstruck/knife A collection of micro-modules (dead, but small self-contained)
https://github.com/bartbes/Class-Commons attempt at unifying class libraries under a common API
https://github.com/iamtimmy/maan Experimental C++ wrapper for LuaJIT’s C API
https://github.com/kikito/middleclass OOP library for Lua
https://github.com/leafo/tableshape Verify (and optionally transform) tables according to a schema
https://github.com/love2d-community/awesome-love2d
https://github.com/lunarmodules/Penlight Large collection of libraries (containers, OOP, input…)
https://github.com/lunarmodules/luacheck Linting and static analysis
https://github.com/samyeyo/rtc Lua script to executable compiler
https://github.com/slembcke/debugger.lua
https://github.com/vrld/hump small collection of tools for developing games with LÖVE

Serialization

Libraries that can output Lua-compatible "code" from data. For serializing tables back into Lua, that maybe can be read using a real, full Lua interpreter (a sort of configuration file format, better than JSON).

https://github.com/Rochet2/smallfolk_cpp C++ implementation
https://github.com/gvx/Smallfolk Deprecated, but mentions other projects, which gives some context
https://github.com/pkulchenko/serpent
https://lunarmodules.github.io/Penlight/libraries/pl.pretty.html

An special case: a C++ library that provides a "table" container which is like a Lua table, and which has good C++/Lua interoperability. * https://github.com/UltraEngine/tableplusplus

Language variants

This is a mixed bag. Some just compile to Lua, some do different things, some are just a different implementation because are written in another language.