I've replaced the Raycaster demo in the Earok's Monkey Demos collection (graphics shamelessly stolen from the classic Amiga FPS Gloom). Now there's rotating, non 90-degree walls, floors, ceilings and kind-of dynamic lighting. Check it out here.

I was kind of developing it for a first person shooter project but I'm not really sure what to do with it now. I'll probably add collision detection and sprites at some point.

As always, the complete Monkey source is on the Monkey Demo's page.