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
A free/open source client and automation tool for Ragnarok Online
Source code repository of the FreeOrion project
Mangos ZERO is a server for World of Warcraft
Open Source MMORPG Framework
Code for Cicero, an AI agent that plays the game of Diplomacy
scene-oriented, flexible 3D engine (C++, Python, C#, Java)
Doom-based AI research platform for reinforcement learning
4X Space Strategy Game
For exploring cellular automata like Conway's Game of Life.
GemRB is a portable open-source implementation of the Infinity Engine
A LinuxSampler Qt GUI Interface
Realism Invictus mod for Civilization IV
Opensource Created Custom Viewers For Virtual Worlds like SecondLife.
Cooperative multiplayer graphical RPG and adventure game
Vivid3D is a C++ IDE/3D engine, with python scripting.
... the open-source glide computer
A fun realistic multiplayer free-and-open-source first-person-shooter!
GameServer is a sophisticated, game server designed for online games