An Open Source DOS emulator to run old DOS games
GemRB is a portable open-source implementation of the Infinity Engine
3D modeler, 3D game maker, 3D demo maker
Android, UIQ 3.0, Series 60 Edition 5 open-source software
A promising chess program
0 A.D. is a free, open-source, cross-platform real-time strategy game.
Free and Open Game Programming Language for Windows and GNU/Linux
God game: wage war from the stone age to the future
Real-time RPG for PC/tablet/phone; multiple quests and random dungeons
Most elegant 2048 puzzle with game fields 4x4 8x8 16x16 for Windows
A cross-platform interpreter for many point-and-click adventure games
Android, DOS, FirefoxOS, Linux, MacOS and Windows all in one..
This is a hacking style game set in the early '80s
2D physics engine for games
cross-platform 2d game engine
A highly modifiable particle-simulation sandbox game
QBall is a simple breakout style game for Android, Symbian and others.