Doom 64 is a not so well known port of Doom for the Nintendo 64. Unlike the ports for other consoles, it's not exactly a port, but a completely new game, featuring completely new levels, textures, sprites, enemies, and a new plot that takes place right after the events of Doom 2, and it's plot strongly suggests to be the prequel to "Doom 2016" as it be considered a reasonable explanation of how the Doom Marine stayed in Hell and became known as the "Doom Slayer" (thus being considered canonical to the series by many fan theories, and being the TRUE Doom 3). In 2003, Samuel "Kaiser" Villarreal was able to extract all textures, sprites and sounds from the N64 ROM and faithfully recreate the levels in the Doomsday engine, thus creating the Doom 64 Absolution TC, and later making Doom 64 EX (an emulator for the ROM for PC). The Doomsday engine is today considered obsolete, and a Doomworld user called Nightside successfully ported all maps to work on GZDoom, but has given up the project.
Brutal Doom 64 aims to continue this project of "porting" (actually recreating from scratch) Doom 64 to GZDoom and Zandronum engines. Unlike Doom 64 EX or Doom 64 Absolution the goal of this project is not to make a 1:1 port of Doom 64 for PC, but to enhance it in every possible way, bringing the satisfying gore and gunplay of Brutal Doom, new sounds and special effects that greatly enhances the oppressive atmosphere of D64, and attempting to include all the content cut from the original game due the cartridge space of the N64.