Attached Link: http://strlen.com/sauerbraten/

Cube or Sauerbraten, realtime level editing, there is no other game that can do that. Sauerbraten is a real gem in my opinion. Did i mention that both are free?

Robert van der Veeke Basugasubasubasu Basugasubakuhaku Gasubakuhakuhaku!! "Better is the enemy of good enough." Dr. Mikoyan of the Mikoyan Gurevich Design Bureau.