3DWorld
3D Procedural Game Engine Using OpenGL
... should build under gcc on linux with some work, but it's been a while since I tried this. I have an old makefile that is out of date, but may not take too much work to fixup and make it usable. Realtime day/night cycle with weather (rain, snow, hail, wind, lightning). Physically based materials with reflection and refraction. Dynamic shadows, ambient occlusion, up to 1024 dynamic light sources, postprocessing effects. Built-in first person shooter game "smiley killer".