A Mac OS X edition of Psychonauts is now available, both on Steam where it is now a SteamPlay game for both Windows and OS X, and through Mac App Store. Thanks Destructoid, where they have the full announcement of this, including word of an accompanying iOS app which is free. Here's a portion:

As of today, Steam users may download a free update to their Psychonauts game which includes--for the first time--achievements, cloud saves, and a slightly modified Meat Circus.

“We are really excited,” said Double Fine President Tim Schafer, “to finally be answering fans’ requests for a more difficult Meat Circus.”

Mr. Schafer was probably joking about that last part, as Meat Circus, one of the original game’s most difficult sections, has been made slightly less punishing in this update.

“Mostly because I’m getting older and it’s hard for me to press buttons that quickly. Hey, don’t forget to mention the achievements!” Schafer added, unnecessarily, because we already mentioned that feature.