FreeDoom

The release of the Doom engine as free software by its creator, idSoftware, has allowed independent developers to create a parallel version that respects the essence of this classic video game. However, Doom’s engine is useless on its own; in order to play, you need a resource file called IWAD that contains all of the game’s data: textures, graphics, sounds, music, enemies, etc. The purpose of FreeDoom is to build a resource file from scratch that stores a completely new game.

FreeDoom consists of 32 scenes and three difficulty levels, all completely original resources that don’t violate the rights of the author of the original game. However, FreeDoom is only an IWAD file, which means you need an interpreter to run the game such as Zandronum or PrBoom.