AssaultCube

AssaultCube, formerly ActionCube, i is a FREE multiplayer first-person shooter game, based on the CUBE engine. Set in a realistic looking environment, as far as that’s possible with this engine, while gameplay stays fast and arcade. This game is all about team oriented multiplayer with fast, arcade gameplay, it’s addictive and fun!

With efficient bandwidth usage, it’s low-latency and can even run over a 56Kbps connection. It’s tiny too, weighing in at a lightweight 40 MB package available for Windows, Mac and Linux. On the correct settings, it can even run on old hardware (Pentium III and above).

website : http://assault.cubers.net

Nexuiz

Nexuiz is a fast-paced 3D deathmatch game with high-end and complex graphics effects. It is intended to be played over the Internet or over a local network. Several different game types, such as classic deathmatch, team deathmatch and capture the flag are available. Though it also supports a single-player mode and playing against the computer. The game brings deathmatch back to the basics, with perfect weapon  balancing and fast paced action, keeping itself away from the current trend of realistic shooters.

Nexuiz is an Arena First Person shooter coming soon to consoles. Nexuiz is fast paced with extremely competitive game play. IllFonic brings Alientrap Software’s Nexuiz to next-gen gaming consoles around the world while staying true to the game play refined over the years through development. IllFonic introduces a new Victorian influenced art style that is simultaneously futuristic and sophisticated. Nexuiz for consoles is powered by CryENGINE 3.

Nexuiz will feature a dynamic mutator system that allows players to change the rules of the match as its being played; as players rank, new mutators become available for them to use. Leader boards are designed for social networking, letting players feel more engaged with the community.

website : http://www.nexuiz.com/

Warsaw

Warsow is a fast paced first person shooter consisting of cel-shaded cartoon-like graphics with dark, flashy and dirty textures. Warsow is based on the E-novel “Chasseur de bots” (“Bots hunter” in English) by Fabrice Demurger. Warsow’s codebase is built upon Qfusion, an advanced modification of the Quake II engine. Set in a futuristic cartoon-like world where rocketlauncher-wielding pigs and lasergun-carrying cyberpunks roam the streets, Warsow is a completely free fast-paced first-person shooter (FPS) for Windows, Linux and Mac OS X.

Speed and movement, that’s what Warsow is all about. Like a true cyberathlete you jump, dash, dodge and walljump your way through the game. Grab those power-ups before your enemy does, plant the bomb before anyone sees you, and steal the enemy’s flag before anyone knows what’s going on!

website : http://www.warsow.net/

Sauerbraten

Much like the original Cube, the aim of this game is not necessarily to produce the most features & eyecandy possible, but rather to allow map/geometry editing to be done dynamically in-game, to create fun gameplay and an elegant engine.

Sauerbraten is a networked fast-paced 3D first-person shooter game. It supports rather modern graphic effects and a some nice graphic details.
The game client also works as the map editor. It is even possible to create and/or edit a map together with other people over a network connection.
Sauerbraten might be considered unsuitable for children.

website : http://sauerbraten.sourceforge.net

Tremulous

Tremulous is a free, open source game that blends a team based First Person Shooter (FPS) game with elements of a Real Time Strategy (RTS) game. Players can choose from 2 unique races, aliens and humans. Players on both teams are able to build working structures in-game like a Real Time Strategy game. These structures provide many functions, the most important being spawning. The designated builders must ensure there are spawn structures or other players will not be able to rejoin the game after death. Other structures provide automated base defense (to some degree), healing functions and much more.

Player advancement is different depending on which team you are on. As a human, players are rewarded with credits for each alien kill. These credits may be used to purchase new weapons and upgrades from the “Armoury”. The alien team advances quite differently. Upon killing a human foe, the alien is able to evolve into a new class. The more kills gained the more powerful the classes available.
The overall objective behind Tremulous is to eliminate the opposing team. This is achieved by not only killing the opposing players but also removing their ability to respawn by destroying their spawn structures.

website : http://tremulous.net