Self-hosted game stream host for Moonlight
A free/open source client and automation tool for Ragnarok Online
Open source clone of the Age of Empires II engine
Code for Cicero, an AI agent that plays the game of Diplomacy
4X Space Strategy Game
An Ubuntu remix for both new and experienced Linux sophisticates
Realism Invictus mod for Civilization IV
GemRB is a portable open-source implementation of the Infinity Engine
Cooperative multiplayer graphical RPG and adventure game
Opensource Created Custom Viewers For Virtual Worlds like SecondLife.
... the open-source glide computer
GameServer is a sophisticated, game server designed for online games
Vivid3D is a C++ IDE/3D engine, with python scripting.
A Wii-like game that can be controlled using a Nunchuk or a phone.
Add and Subtract game
Janken - A Simple Rock, Paper, Scissors Game
BARS - a program for playing checkers
The AWS GameKit Plugin for Unreal