The Cube shooter

Cube is an open source multiplayer and singleplayer first person shooter

game built on an entirely new and very unconventional engine. Cube is a

landscape-style engine that pretends to be an indoor FPS engine, which

combines very high precision dynamic occlusion culling with a form of

geometric mipmapping on the whole world for dynamic LOD for configurable

fps & graphic detail on most machines. Uses OpenGL & SDL.