Total conversion
From Doom Wiki
A total conversion (TC) is a PWAD that replaces all or almost all of the resources used within the original game. The first total conversion was the Aliens TC developed by Justin Fisher. Other well-known examples of total conversions include Batman Doom, HacX and Action DOOM.
Freedoom is not a total conversion, but the project intends to replace every resource in the Doom and Doom II IWADs.
