First-person shooter game

Aliens vs Humans, First Person Shooter game with elements of Real Time Strategy

Tank digging battle game

Leading the way in newschool multiplayer Doom online

Top-down shooter action RPG

Open source first person shooter

Dhewm 3 is a Doom 3 GPL source port

ReC98 source port of the first Seihou Project game

Epic story-driven FPS running on the Build Engine

The Free and Fast Arena Shooter

Yamagi Quake II is an alternative client for id Software's Quake II

Free fast paced arena shooter

Game engine for Classic Doom

Open Source voxel shooter

Free agile arena shooter

Classic arena first person shooter

A Quake mod based on the retro shooter SPRAWL

Shoot and survive

FPS aim trainer

Fast paced, first person strategy game

Game engine for Return to Castle Wolfenstein

Source port for Build engine games

a modern QuakeWorld client focused on competitive online play

Modern cross-platform port of the Descent engine

A Zandronum 3.0 fork with improved netcode, configurable movement and many small tweaks

First-person shooter with cooperative in-game map editing

A modern cross‑platform port of “STAR WARS™: Dark Forces” with mod support

The orb ponderer's arena first-person shooter

A modernization effort of DOOM-3-BFG

EDuke32 is an awesome, free homebrew game engine