Fast paced, first person strategy game

First-person shooter game

Free fast paced arena shooter

The Free and Fast Arena Shooter

Open source first person shooter

Game engine for Classic Doom

Classic arena first person shooter

Open source first person shooter

Tank digging battle game

dhewm 3 is a Doom 3 GPL source port

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

Leading the way in newschool multiplayer Doom online

Top-down shooter action RPG

A modernization effort of DOOM-3-BFG

Free agile arena shooter

Modern cross-platform port of the Descent engine

Epic story-driven FPS running on the Build Engine

First-person shooter with cooperative in-game map editing

Open Source voxel shooter

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

A Quake mod based on the retro shooter SPRAWL

Shoot and survive

Game engine for Return to Castle Wolfenstein

FPS aim trainer

Source port for Build engine games

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

The orb ponderer's arena first-person shooter

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

EDuke32 is an awesome, free homebrew game engine

ReC98 source port of the first Seihou Project game