Monkeystein is a mod for registered Wolfenstein, made by Ian Summerfield. It was released on July 18, 2003.
It features 31 levels, plays in episodic flow and guarantees the player an ape-tastic adventure. Many graphics have been changed, and features new guards guaranteed to drive the player bananas.
The EXE used is that of Mallenstein; this is most likely because Summerfield did not own the actual Wolfenstein 3D EXE. No extra features are needed as such, and it can be played in SDL without any trouble using the original Wolfenstein EXE.