A simple turn-based artillery game and also a real-time strategy game.
Commander Keen Interpreter
Spring is a free RTS engine developed for Windows, Linux and Mac OS X.
Sims 3 (and other) game package library
Console based rcon client for minecraft servers.
A MUD client for Android, iOS, Linux, Mac OS X and Windows
DOOM / Heretic / Hexen source port with enhanced graphics and UI
Arianne is an engine to develop multiplayer online games like Stendhal
xBRZ: "Scale by rules" - high quality image upscaling filter by Zenju
Open source model airplane simulator
Ur-Quan Masters High Definition
The Sokoban game implemented in Java.
Pioneers - The Settlers of Catan
Real Time Strategy game engine supporting early Westwood classics