Final Doom consists of two 32-level megawads (level files) , TNT: Evilution by TeamTNT and The Plutonia Experiment by the Casali brothers. TNT: Evilution features a new soundtrack, while The Plutonia Experiment uses music from Doom and Doom II.
Work on TNT: Evilution was started by TeamTNT, a group of WAD-making hobbyists who were active on the advanced Doom editing mailing list. Just days before it was to be released as a free download online, the project was acquired by id Software, and finished in November 1995. Many people were angry about Id's decision to include Evilution in Final DOOM - as it was originally going to be released as a freeware expansion onto DOOM II.