0 A.D. is a free, open-source, cross-platform real-time strategy game.
Pycraft is an open-source, OpenGL based game made in Python
A free 3D game engine to create games and realtimes scenes for Windows
Open source FPS/RTS Game
2D Game Engine
3D-Accelerated open-source DOOM engine
Java 2D graphics/utility library
Small OpenGL based game enegine
Vehicle simulation with freedom of movement on large map (5x5km).
3D game engine for C and C++
A graphics engine + toolkit.
Pear3DEngine is a modern and modular 3D development framework
Echoes Entertainment's game engine
CM Game Development Kit