Free Sci-Fi online FPS games

This second list includes free online first-person shooters that are unrealistic and usually set in the future. These FPS's often have similarities to shooters like Quake or Unreal Tournament. Most of them have relatively fast-paced gameplay and fictional weaponry like gravity guns and plasma weapons. There are around 10 games in this list that also have Linux and/or Mac versions. Some shooters may have very low player base or no players at all.

Team Fortress 2

Team Fortress 2 is a team-based multiplayer first-person shooter that recently became a free-to-play game. This shooter has cartoon style graphics and nine different player classes.

System requirements: 1.7 GHz CPU, 512MB RAM, DirectX 8.1 level graphics card.

http://www.tf2.com/  (also available for Mac)

Quake Live

Quake Live is a browser-based variant of famous online first-person shooter, Quake III Arena. Some arenas, game types and server options are not available for free users.

System requirements: 800 MHz CPU, 512MB RAM, NVIDIA GeForce4 MX / ATI Radeon 8500.
http://www.quakelive.com/  (also available for Linux and Mac)

Half-Life 2: Deathmatch

Half-Life 2: DM is a fast multiplayer first-person shooter where you can also throw objects with gravity gun. Half-Life 2: Deathmatch is only free for ATI and NVIDIA graphics card users.

System requirements: 1.2 GHz processor, 256MB RAM, DirectX 7 level graphics card.
ATI , NVIDIA 

F.E.A.R. Combat

F.E.A.R. Combat is a free stand-alone multiplayer component of F.E.A.R., the horror themed first-person shooter. You have to register a free CD-Key to join F.E.A.R. Combat.

System requirements: 1.7 GHz Pentium 4, 512MB RAM, 64MB GeForce 4 Ti / Radeon 9000.
http://projectorigin.warnerbros.com/fearcombat/

Wolfteam

Wolfteam is a fast-paced MMOFPS with many special features - like ability to transform into a werewolf. Wolfteam has large assortment of modern weaponry and 7 game modes.

System requirements: 1.4 GHz Pentium 4, 512MB RAM, GeForce 5700 or higher.
http://wolfteam.softnyx.net/ , http://wolfteam.aeriagames.com/

Xonotic

Xonotic is a free open source fast-paced first-person shooter that is direct successor of the Nexuiz Project. Xonotic features new physics, maps, player models and animations.

System requirements: unknown, similar to Nexuiz.
http://www.xonotic.org/  (also available for Linux and Mac)

Mars War

Mars War is a free-to-play Sci-Fi MMOFPS with huge maps that can contain hundreds of real players. Mars War has wide variety of robots, equipments and vehicles (tanks, spaceships).

System requirements: Pentium IV 2.0 GHz, 1GB RAM, Geforce 6200 / Radeon 9550.
http://marswar.mmolover.com/

Nexuiz

Nexuiz is a free fast-paced cross platform first-person shooter, which runs on DarkPlaces engine. Nexuiz also includes a relatively short single-player campaign with bots.

System requirements: 1 GHz Pentium III or AMD Athlon, 512MB RAM, GeForce 2.
http://www.nexuiz.com/classic.php  (also available for Linux and Mac)

Warsow

Warsow is a multiplayer free FPS set in a cartoonish world. Warsow's gameplay focuses on fast movements and tricksjumps (such as bunny hopping, wall jumping, rocket jumping...).

http://www.warsow.net/  (also available for Linux and Mac)

Alien Arena 2011

Alien Arena is a retro Sci-Fi multiplayer FPS based on the CRX engine. Alien Arena 2011 has wide set of fun and unique weapons, dozens of maps, various play types and accessories.

System requirements: 1GHz CPU, 256MB RAM, OpenGL compatible graphics card.
http://red.planetarena.org/  (also available for Linux and Mac)

Celestial Impact

Celestial Impact is a team based multiplayer first-person shooter that takes place on asteroids floating in space. It features destructible world and ability to add terrain to the landscape.

System requirements: 2 GHz CPU, 512MB RAM, 128MB GeForce 6000 series or equivalent.
http://www.celestialimpact.com/

World of Padman

World of Padman is a cartoony free FPS game set in the miniature world of Padman. WoP has over 23 richly detailed maps, each supporting up to seven different play modes.

System requirements: 1 GHz CPU, 512MB RAM, 128MB OpenGL Video Card.
http://www.worldofpadman.com/  (also available for Linux and Mac)

Sauerbraten

Sauerbraten is a free first-person shooter similar to Quake. Sauerbraten features both single-player and multiplayer modes, it also includes a dynamic ingame level editor.

System requirements: 733 MHz CPU, 128MB RAM, 32MB GeForce 2 MX.
http://www.sauerbraten.org/  (also available for Linux and Mac)

Tremulous

Tremulous is a free game that blends team-based FPS with real-time strategy elements. This shooter features two teams: humans and aliens, both teams can build in-game structures.

System requirements: 800 MHz CPU, 256MB RAM, NVIDIA GeForce 4 / ATI Radeon 9200.
http://www.tremulous.net/  (also available for Linux and Mac)

OpenArena

OpenArena is a free open-source clone of Quake III Arena. The gameplay is basically identical to the shooter it's based on, even some Quake 3 mods work with OpenArena.

System requirements: Pentium II 233 MHz, 64MB RAM, 16MB OpenGL video card.
http://openarena.ws/  (also available for Linux and Mac)

UberStrike

UberStrike is a free-to-play cross-platform online first-person shooter, available for both Mac and Windows PC. UberStrike is the world’s first browser-based MMOFPS.

http://uberstrike.cmune.com/  (also available for Mac)

Red Alert: A Path Beyond

Red Alert: A Path Beyond is a first-person shooter based on classic real time strategy, Command & Conquer: Red Alert. This shooter is standalone and free to play.

System requirements: 800 MHz CPU, 128MB RAM, 32MB DirectX 7 compatible video card.
http://www.apathbeyond.com/

Legions: Overdrive

Legions: Overdrive is a free Sci-Fi FPS based on cancelled project, Fallen Empire: Legions. Many gameplay elements in Legions: Overdrive are borrowed from the Tribes series.

System requirements: 2.2 GHz Pentium 4, 512MB RAM, NVIDIA GeForce 6800 / 8400.
http://www.legionsoverdrive.com/

SCUD Storm

SCUD Storm is a freeware game that turns Command and Conquer: Generals - Zero Hour into a 3D first-person shooter. SCUD Storm is standalone, you don't need any game to play this.

http://www.moddb.com/games/scud-storm

Starsiege: Tribes

Starsiege: Tribes is a multiplayer Sci-Fi first-person shooter with no single-player campaign. It was released for free to promote the release of Tribes: Vengeance, the upcoming sequel.

System requirements: Pentium 166 MHz, 32MB RAM, 3D graphics accelerator.
http://www.planettribes.com/

Tribes 2

Tribes 2 is a sequel to Starsiege: Tribes, set in the year 3941. Tribes 2 is a completely free to download multiplayer first/third-person shooter that takes place in fictional Earthsiege universe.

System requirements: Pentium II 500 MHz, 64MB RAM, 12MB video card.
http://www.tribesnext.com/ 

Legends

Legends is a fast-paced freeware online first-person shooter with jetpacks, similar to Tribes. This shooter also has mission editor and terrain generator integrated into the game engine.

http://legendsthegame.net/  (also available for Linux)

Galacticwar

Galacticwar is a free Sci-Fi first-person shooter that features both single-player and multiplayer modes. Galacticwar (GCW) will have single-player campaign and vehicles in the future.

http://www.moddb.com/games/galacticwar

Daikatana Deathmatch

Daikatana Deathmatch is a free and non-profit fan made multiplayer modification of Daikatana. This modification is multiplayer only and have all single-player maps removed.

Minimum requirements: Pentium 233, 32MB RAM, 4MB OpenGL compliant video card.
http://www.daikatananews.net/

Transfusion

Transfusion is a free to download online first-person shooter that aims to be a total remake of Monolith's Blood. This multiplayer only shooter is based on the DarkPlaces engine.

http://www.transfusion-game.com/  (also available for Linux)

Control Monger

Control Monger is a free Sci-Fi first-person shooter in which you take control of a robot. Control Monger features seven player types and support for LAN play.

System requirements: 1.5 GHz CPU, 256MB RAM, 3D capable card 64MB video card.
http://www.controlmonger.com/

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