A modernization effort of DOOM-3-BFG

Shoot and survive

First-person shooter game

Top-down shooter action RPG

Leading the way in newschool multiplayer Doom online

Modern cross-platform port of the Descent engine

Classic arena first person shooter

Epic story-driven FPS running on the Build Engine

Source port for Build engine games

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

The Free and Fast Arena Shooter

Open Source voxel shooter

Tank digging battle game

Free fast paced arena shooter

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

Free agile arena shooter

First-person shooter with cooperative in-game map editing

FPS aim trainer

Open source first person shooter

Game engine for Classic Doom

Fast paced, first person strategy game

Game engine for Return to Castle Wolfenstein

Open source first person shooter

dhewm 3 is a Doom 3 GPL source port

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

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

a modern QuakeWorld client focused on competitive online play

A Quake mod based on the retro shooter SPRAWL

EDuke32 is an awesome, free homebrew game engine

The orb ponderer's arena first-person shooter