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
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
... the open-source glide computer
4X Space Strategy Game
GLScene Engine for Delphi & C++Builder VCL Windows 32/64
3D modeler, 3D game maker, 3D demo maker
Opensource Created Custom Viewers For Virtual Worlds like SecondLife.
Realism Invictus mod for Civilization IV
For exploring cellular automata like Conway's Game of Life.
GemRB is a portable open-source implementation of the Infinity Engine
Cooperative multiplayer graphical RPG and adventure game
A Sudoko Solver/Puzzle Generator For MS Windows
Vivid3D is a C++ IDE/3D engine, with python scripting.
GameServer is a sophisticated, game server designed for online games
With the helpfull nef, you have to rescue earthlike planets!