Guystein is a Wolfenstein 3D mod by Guy Brys released in February of 2000.
The actual maps of the game are locked in a separate zip which needs a password to unlock. The original intention was that players would email Guy and he would send them back the password, but obviously such a system has a finite longevity. Thankfully Guy included a hint to figuring out the password in a text file. The password is "Shapiro-Wilk" (without quotes).