Epic story-driven FPS running on the Build Engine

Dhewm 3 is a Doom 3 GPL source port

EDuke32 is an awesome, free homebrew game engine

Top-down shooter action RPG

Free agile arena shooter

Free fast paced arena shooter

The Free and Fast Arena Shooter

Fast arcade first person shooter

Open Source voxel shooter

A modernization effort of DOOM-3-BFG

Modern cross-platform port of the Descent engine

Leading the way in newschool multiplayer Doom online

First-person shooter game

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

Classic arena first person shooter

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

Fast paced, first person strategy game

Tank digging battle game

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

Source port for Build engine games

The orb ponderer's arena first-person shooter

Open Source voxel shooter

Open source first person shooter

a modern QuakeWorld client focused on competitive online play

A Quake mod based on the retro shooter SPRAWL

FPS aim trainer

ReC98 source port of the first Seihou Project game

Game engine for Classic Doom

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

Game engine for Return to Castle Wolfenstein