
Crytek’s first online FPS called Warface is a military shooter in a near future setting. It offers a cinematic experience with next gen visuals, AI and physics based on Crytek’s proprietary CryENGINE® 3 game development solution. Warface provides gamers with a constantly updated extensive PVE universe full of dramatic multiplayer co-op missions, a full set of class based PVP and will be available for PC. This new Crytek IP is especially dedicated to the Korean and other Asian markets and is co-produced by Crytek Seoul. Warface is supported by a free-to-play business model.

Offensive Combat is a free-to-play, browser-based first-person shooter. Interests include stabbing trolls in the neck with wooden swords, shooting asshats in the face with a variety of ballistic and plasma-based weapons, and pwning the hell out of anyone who falls before us with a variety of silly little dances. Lizard men in Hawaiian shirts and robots disguised as bananas!

-Gotham City Impostors is a download-only multiplayer FPS that pits violent vigilantes dressed up like Batman against craven criminals dressed up like the Joker in open warfare on the streets of Gotham City.
-In the future, the last survivors of the Great War continue their fight with the ultimate war machine: the AirMech. Created using lost technology, Pilots have found, salvaged, or stolen AirMechs that they use to protect the weak, or to pillage. Which side do you fight for?
And many more free to play will be on Steam in the next months.. Also worth mentioning 2 games you have already seen on g4g.it – Bullet run and Super Crate Box

UPDATE:According to an user comment below in this page, Ace of Spades is no more free, it is now a commercial game. However there is a free version named Build and Shoot based on the same engine..
Here is the link to Build and Shoot
Ace of Spades is the best bits of Minecraft crossed with the fast-paced shooter gameplay of Team Fortress. Free and runs on any PC.