HTML5 Phigros chart player/simulator
RPG Maker 2000/2003 and EasyRPG games interpreter
Aim assistance for blocks and mobs
Open-source Android/Desktop remake of Civ V
Open-source rhythm game
An open source re-implementation of RollerCoaster Tycoon 2
Archipelago Multi-Game Randomizer and Server
One of the best Prodigy hacks
Doom-based AI research platform for reinforcement learning
A game of dungeon exploration, combat and magic
Classic overhead run-and-gun game
Access GameLift resources and integrate GameLift into your Unity game
Endless Sky is a sandbox-style space exploration game
You can make it - Open Source MMORPG Platform
Voxel game-creation platform with easy modding and game creation
The Shiptest Codebase
The Oldschool Runescape API wrapper that does more
The Ren'Py Visual Novel Engine
Multi Theft Auto is a game engine
Fully async, multithreaded, predictive, open source, 3.01 reach
Build multiplayer web games played by millions
Widelands is a free, open source real-time strategy game
Minecraft map editor and mod
Free and open source real-time strategy game
3D space trading and combat game