Frozenbyte has announced that a set of free DLC for Trine is now available, and will be applied automagically once you fire up your Steam client on the PC. There's no details on exactly what's in the content, called "Path to New Dawn," only that it'll be unlocked for players once they complete the game.
The DLC also includes a patch which fixes various bugs for the game. Owners of the retail copy of Trine will be getting the update later this week. Currently it seems PlayStation owners will not be getting the patch or new content, though Frozenbyte would like to bring it eventually.