Wolfenstein 3D was originally released as shareware, which allowed it to be copied widely. The shareware release contained 1 episode, consisting of 10 missions (levels). The commercial release consisted of 6 episodes, including the shareware episode. Each episode had a different "boss" which had to be killed in the final mission in order to complete the episode. In order to complete an episode, only 9 of the 10 missions needed to be completed. Hidden in one of the first eight missions was an entrance to a secret level.
An expansion pack, Spear Of Destiny, was also released.
The game was originally released on the PC and then ported to Macintosh computers, Apple IIGS, Super NES, and Atari Jaguar. The source code of the game was published by ID Software in 1996.
To render the walls in pseudo-3D, the game used [ray casting]?, a special case of ray tracing that sent out one ray for each column of pixels, checked if it intersected a wall, and drew textures? on the screen accordingly, creating a depth buffer against which to clip the scaled sprites that represented enemies, powerups, and props.
A new first-person shooter, [Return To Castle Wolfenstein]?, a loose sequel (though with the advance of technology the graphics and gameplay are vastly different), has been released. It uses the Quake III Arena graphics engine.