Shooter
Shooter games are a sub-genre of action games, which often test the player's speed and reaction time. It includes many subgenres that have the commonality of focusing "on the actions of the avatar using some sort of weapon. Usually this weapon is a gun, or some other long-range weapon. Read the full article at the Wikipedia.
Running with Rifles
(2 Apr 2015)RUNNING WITH RIFLES is a top-down sandbox shooter, with emphasis on cooperation, squad leading and being a tiny soldier in a big war.
Genre: Shooter, Action 
Snorms
1.1.2 (22 Oct 2012)Snorms is a third person (isometric) shooter game featuring dozens of upgradeable weapons, dozens of levels full of monsters, leveling...
Genre: Arcade, Shooter 
Unvanquished
Alpha 50 (14 Apr 2016)Unvanquished is a first-person shooter and strategy game created by Unvanquished Development.
Genre: Shooter, Strategy, Action 
AirMech
by Carbon Games
frequently updated
(4 Dec 2012)
AirMech is a Herzog Zwei-like action-strategy game that puts you in the battle as a giant transforming robot!
From the air, build...
Genre: Shooter, Strategy, Action 
Retro Blazer
by Amil Parra
RB010912
In the vast labyrinth of ARK Island, once elder now Tyrannical Warlord, Lokahndril, has used the island's ancient mainframe entity...
Genre: Shooter, Action 
3089
1.3.3 (13 Dec 2012)3089 is a futuristic, procedurally generated, open-world action role-playing game.
Genre: Shooter, Stealth, Adventure, Role-playing, Action 
Fade to Black
f2bgl (24 Nov 2011)Fade to Black is the sequel to Flashback.
Genre: Shooter, Adventure, Action 
Vore Tournament
0.7 (19 Mar 2012)A furry vore game forked from the Nexuiz project.
Genre: Shooter, Action 
Wolfenstein 3D
by id Software
1.7
Maybe it was the fact that people got to blow away Nazis.
Genre: Shooter, Action 
Unreal Tournament
by Epic Games
436
(8 Nov 2000)
Unreal Tournament is a game that provides the ultimate in multiplayer excitement whether you're hooked up to the Internet or not.
Genre: Shooter, Action 
Eternal Damnation
6.2 (7 Nov 2007)Eternal Damnation is a fan-produced mod that RWS included in its Fudge Pack compilation.
Genre: Shooter, Total conversion, Action 
Unreal
by Epic Games
227i
(11 Nov 2012)
Unreal takes place about 200 years from now.
Genre: Shooter, Action