The source code to VVVVVV
UCI chess engine
3D modeler, 3D game maker, 3D demo maker
Embeddable unity game engine view for Flutter
2D game development library for Ruby and C++
Web-based Cloud Gaming service for Retro Game
plugin-based RPG manager in C++ and Qt5
Cross platform 2D/3D game engine written in C++11 & OpenGL ES 2/3
Make games with Lego-like building blocks