Sauerbraten

[Treewyrm]

Mmmm im not much of a fan of the Cube series of games, If its real time level editing your after take a peek at halo3 or garrys mod for hl2

Neither halo 3 forge nor garry's mod are map editors, they are tools to modify objects on existing map(s), not to create new maps. Sauerbraten features complete WYSIWYG map editor inside the game, just push edit button and you're edit mode, can modify geometry and do whatever you please, then push play button and you're back into the game with all modifications you made on it. I've been using map editors since the days of Wolfenstein 3D and made maps for various games, but this thing made me exciting. Epic Games have mentioned UT3 and it's UE3 version will feature somewhat similar WYSIWYG functionality. You can leave Halo 3 Forge and GMod to kids to play with physics and weapon balance on the maps, the real level design is about complex and stylish architecture tied to gameplay.