Dwarf Fortress 2012 has been released! After DF2010 [mefi], Toady One had planned to keep up a regular schedule of smaller releases. But while adding 300+ animals from a fundraising drive, the feature set spiralled beyond expectation. [more inside]
Killer Carp. Magma. Fire-breathing Capital D's. A new version of the cult rougelike/fantasy world sim Dwarf Fortress was released today. It's a windows only download - there should be Mac and Linux versions out in a week or so. Here's what tvtropes has to say about the game. Previously on metafilter: 1 2 3 4
Dwarf Fortress is the best game you haven't played yet. A rogue-like crossed with Civilization/Dungeon Keeper, freely available (although in Alpha), completely random and incredibly deep. The Wiki will help you get started.