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 exclusive Portal 2 downloadable content available to owners of the Razer Hydra (Purchasable on the Steam store). The DLC includes specific levels and mechanics that make use of the Razer Hydra's motion detection capabilities.

Peer Review
Portal 2 was set to receive a free DLC in Summer 2011 but unfortunately it became a victim of Valve Time. The DLC is expected to introduce Challenge Mode for Singleplayer and Co-op, Leaderboards , and a whole new Co-op course. In the September 30th blog post, Valve announced the DLC to be called 'Peer Review' and will be released on Wednesday 5th October.

Portal 2 in Schools
During Gabe Newell's keynote at the Games For Change festival, Gabe mentioned that Valve were beginning working with schools to build curricula around Portal 2; looking into, as Stephen Totilo of Kotaku summarised, "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.