Godot is a powerful cross-platform game engine
A certain block game
An open-source sandbox tower defense game
A simple and easy-to-use library to enjoy videogames programming
Xash3D FWGS engine
Stream switch games to your PC via USB or network
A cross-platform PSP emulator
UCI chess engine
Cocos simplifies game creation and distribution with Cocos Creator
Open source cross-platform multi-purpose game toolkit
Desktop/Android/HTML5/iOS Java game development framework
RetroArch is a frontend for emulators, game engines and media players.
Sandbox video game with a powerful physics engine
The game engine for everyone
Open source voxel game engine with support for survival and crafting
The source code to VVVVVV
Home theater software and entertainment hub for digital media
Do virtual gear shifting (and more) in any rider app
One framework for creating powerful cross-platform games
Open-source Android/Desktop remake of Civ V
Open source HTML5 game framework that offers WebGL and Canvas
Voxel game-creation platform with easy modding and game creation
Free, cross-platform 2D game engine powered by Haxe and OpenFL
A dead simple 2D game engine for Go
An open source reimplementation of the Among Us Server