Epic story-driven FPS running on the Build Engine

Free fast paced arena shooter

Dhewm 3 is a Doom 3 GPL source port

Open source first person shooter

Open source first person shooter

First-person shooter with cooperative in-game map editing

ReC98 source port of the first Seihou Project game

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

A modernization effort of DOOM-3-BFG

Tank digging battle game

The orb ponderer's arena first-person shooter

Fast paced, first person strategy game

Shoot and survive

Modern cross-platform port of the Descent engine

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

FPS aim trainer

Open Source voxel shooter

Classic arena first person shooter

A Quake mod based on the retro shooter SPRAWL

EDuke32 is an awesome, free homebrew game engine

Fast arcade first person shooter

Top-down shooter action RPG

Game engine for Classic Doom

Free agile arena shooter

The Free and Fast Arena Shooter

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

Game engine for Return to Castle Wolfenstein

a modern QuakeWorld client focused on competitive online play

Open Source voxel shooter

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