The Super Nintendo version of Doom was published by Williams Entertainment on September 1, 1995, near the end of the system's life cycle. This is the first SNES title rated M for mature, and one of only three rated as such (the others being Mortal Kombat 3 and Ultimate Mortal Kombat 3, coincidentally also published by Williams Entertainment, Inc.). The cartridge features a Super FX 2 chip, and Doom was one of few SNES games to feature a colored cartridge; the NTSC release was available in a red casing. The game does not use the Doom engine, but features a custom engine, known as the Reality engine, programmed by Randy Linden.