The flexible game engine
Xash3D FWGS engine
A completely free, open-source, 2D game engine
Orx: Portable Game Engine
A modern, cross-platform Quake game engine based on FitzQuake.
Game engine to build text adventures.
A cross-platform, open-source, pure C game engine for mobile game
Cross-platform 2D and 3D game engine
Game engine for playing tomb raider 1 - 5 levels.
A basic 3D environment with a first-person POV