Portal 2

Portal 2 is the sequel to the award winning and hugely successful Portal developed by Valve Corporation. It features a single-player story set after the events of Portal's story; and a brand-new Co-op game mode, featuring additional test chambers designed specifically for Co-operative play. Portal 2 was released April 19, 2011 on the Steam platform. North America got retail release on the April 19, 2011; Europe and Australia, April 21, 2011.

Sixense
The Portal 2 Sixense MotionPack DLC is an exclusive DLC available to owners of the Razer Hydra. The DLC includes specific levels and mechanics that make use of the Hydra's motion detection functionality.

Peer Review
Peer Review is the first DLC released for Portal 2. Released on October 4th, 2011; this DLC introduces Challenge modes for both single-player and co-op, a leaderboards system, and a mini-hub area reserved for additional co-op tracks. This DLC adds the first of many additional courses to come with the introduction of the Art Therapy testing course.

Portal 2 in schools
During a keynote presentation at the festival in 2011, Valve director Gabe Newell mentioned that the company was beginning to work with schools to build curricula around Portal 2, looking into "how to teach attraction, repulsion... [they] need to be clear on what their metrics are... what the outcome is, what they're optimizing for".

Trivia

 * Shooting a portal to the moon as the ending was originally an easter egg "3 minutes into the game", which caused the player to be sucked out of the test chamber and die - and was an alternate game ending.