[sfx1999]

Originally Posted by Whistler

there are also some "cloned" Quake3 engines, may be useful for you:
http://hkitchen.quakesrc.org
http://www.planetquake.com/qbism

I already know that they are engines like that. But you forgot:

Cake
Disesel

They are basically map viewers. Then there is a project not yet released called Tenebrae 2.0. It looks awesome.