Sort of like Wolf3D, but more ... wacky. It was created by Ken Silverman (who later went on to design the "Build" engine used for Duke3D). Originally he released it on his own ... later it was purchased by Epic Megagames, although I liked the original better. It's still fun to play even though it uses outdated technology, and it's more likely to work on your computer than Wolf3D is. :) (NOTE: This is the full registered version of the game! It has been released for free by the original author, Ken Silverman.)