Freedoom

Phase 1 is the first part of the single-player game, containing four episodes which are nine levels each, smoothly paced for beginner players. It is compatible with mods for the original Doom and The Ultimate Doom.

Phase 2 is the second major part of the single-player game, a massive 32-level episode expanding upon the same concepts present in Phase 1, as well as containing additional monsters and the double-barreled shotgun! The levels in this game tend to demand more skillful play than the previous episodes. It is compatible with mods for Doom II.

FreeDM is a fast-paced competitive deathmatch game, part of the Freedoom project. Rather than the usual single-player focused levels, these contain no monsters and are intended for deathmatch only. It is compatible with mods for Doom II.

Crispy Doom preserves most of the original Doom engine’s classic look and feel while adding many quality-of-life modernizations. Its parent project, Chocolate Doom, is much more faithful to the original DOS Doom but is not recommended for ordinary use as it replicates some unstable behavior.

Eternity Engine is a feature-rich engine with a significant amount of customizability for more advanced level and gameplay modifications.

GZDoom is an advanced Doom-engine-based general game development platform with enormous customizability for both authors and players. Many mods released for Doom and Freedoom have been developed around its unique features. It does, however, deviate significantly from the original Doom gameplay and aesthetics and cannot play any gameplay recordings (“demos”) that would otherwise work with the Doom engine.