3D game engine/framework in C, with Luajit and Python bindings now
Orx: Data-Driven Game Engine
SDL based generic 2D game engine
Cross-platform 2D and 3D game engine
An Adventure Game Engine
3D Game Engine
A basic 3D environment with a first-person POV
Small OpenGL based game enegine
3D game engine for C and C++
A DirectX based graphics/physics engine