Self-hosted game stream host for Moonlight
Open source clone of the Age of Empires II engine
Powerful, mature open-source cross-platform game engine for Python
Simple and Fast Multimedia Library
Environments and algorithms for research in general reinforcement
Code for Cicero, an AI agent that plays the game of Diplomacy
Source code repository of the FreeOrion project
A free/open source client and automation tool for Ragnarok Online
Frame profiler
The Arcade Learning Environment (ALE) -- a platform for AI research
scene-oriented, flexible 3D engine (C++, Python, C#, Java)
Doom-based AI research platform for reinforcement learning
4X Space Strategy Game
Cooperative multiplayer graphical RPG and adventure game
GemRB is a portable open-source implementation of the Infinity Engine
Opensource Created Custom Viewers For Virtual Worlds like SecondLife.
Vivid3D is a C++ IDE/3D engine, with python scripting.
For exploring cellular automata like Conway's Game of Life.
Realism Invictus mod for Civilization IV
... the open-source glide computer
GameServer is a sophisticated, game server designed for online games
Janken - A Simple Rock, Paper, Scissors Game