Epic story-driven FPS running on the Build Engine

Dhewm 3 is a Doom 3 GPL source port

Shoot and survive

Open Source voxel shooter

Leading the way in newschool multiplayer Doom online

Modern cross-platform port of the Descent engine

Tank digging battle game

Free fast paced arena shooter

Lo sparatutto arena libero e veloce

Source port for Build engine games

Classic arena first person shooter

Game engine for Classic Doom

A free first person shooter for Mac, PC and Linux

Free agile arena shooter

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

First-person shooter game

FPS aim trainer

Game engine for Return to Castle Wolfenstein

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

EDuke32 is an awesome, free homebrew game engine

Open source first person shooter

First-person shooter with cooperative in-game map editing

Open source first person shooter

a modern QuakeWorld client focused on competitive online play

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

A Quake mod based on the retro shooter SPRAWL

A modernization effort of DOOM-3-BFG

Fast paced, first person strategy game

Top-down shooter action RPG

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