| The Unreal Engine, developed by Epic Games is getting on for 3 or 4 years old now. It was initially developed by Tim Sweeney (I think). As mentioned above, it has some serious limitations due to the hardware that it was originally designed to exploit (First gen Pentium MMX processors and 3Dfx Voodoo cards). Particularly annoyingly, it has a very sucky visibility algorithm which places a tight limit on the number of faces you can have in a scene (and sometimes leads to large numbers of polys still being calced even if they are obscured by a wall). However, the fact that the engine was able to power commercial games for such a long time shows thta it was a fairly formidible piece of technology. A heavily revised version with nice features like dynamic level of detail was used in Unreal Tournament and Deus Ex. As well as pumping out 3D, these games had a fully functional 2D GUI toolkit as well. Epic have mentioned on occasion that they wish they hadn't named the engine and the first game to use it 'Unreal' as people still equate the engine (soon to be released as the totally new Unreal 2.0) to the first game. There is a list of all the projects that have used this engine at : http://www.unrealengine.com/engine/ | 
