Doom is described as 'Science fiction horror-themed first-person shooter video game in which players assume the role of a space marine, popularly known as "Doomguy", who must fight his way through the hordes of invading demons from Hell' and is a popular first-person shooter in the games category. There are more than 50 games similar to Doom for a variety of platforms, including Windows, Linux, Mac, Steam and Playstation apps. The best Doom alternative is Half-Life. It's not free, so if you're looking for a free alternative, you could try Xonotic or AssaultCube. Other Doom like games are Quake, Fallout, Borderlands and GZDoom.
Alien Swarm is a free top-down shoot-em-up video game by Valve Corporation. It is a remake of the Alien Swarm mod for Unreal Tournament 2004, and it was developed by the original team, which was hired by Valve during the course of the development process.
Set in the iconic Alien universe, Aliens: Fireteam Elite is a cooperative third-person survival shooter that drops your fireteam of hardened marines into a desperate fight to contain the evolving Xenomorph threat.
Excalibur: Morgana's Revenge is a first-person action shooter game that combines time travel to take the player through the Jurassic period, Camelot period, and into the future chasing down Morgana.
Free online shooter featuring multiple game modes, customizable weapons, numerous maps, both PvP and PvE gameplay, clan wars, and regular updates. Offers character personalization, dynamic events, leaderboards, and fast-paced, tactical multiplayer combat.
Wolf Team is a fast paced 3D MMOFPS that features the ability for players to transform between playing as a Human or as a Werewolf. Humans have an assortment of weapons available at their disposal giving them an advantage at a distance.
Fortress Forever is a free game inspired by the earlier versions of the Team Fortress series (Team Fortress Classic and QuakeWorld Team Fortress).
Take part of history’s greatest battle of Green VS. Tan. Fight amongst and against others online. Sometimes the greatest battles are fought by the smallest of soldiers.
You are John Blade, commander of HardCorps, an elite security force dedicated to protecting the people of Freeport City. Four years have passed since your first battle with Elexis Sinclaire, a beautiful, brilliant, and ruthless scientist who is out to remake humanity according...
Natural Selection 2 is a RTS/Shooter/Biter that you either play as marines or aliens, it is currently under development by Unknown Worlds.
Tremulous is a free, open source game that blends a team based FPS with elements of an RTS. Players can choose from 2 unique races, aliens and humans. Players on both teams are able to build working structures in-game like an RTS.
Mafia is a series of action-adventure video games developed by 2K Czech (formerly Illusion Softworks) with the third installment by Hangar 13, and published by 2K Games.
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It's a 3rd person, story-driven action game, while Doom is a 1st person arcade game.