Valve has announced that Portal 2 DLC, entitled Perpetual Testing Initiative, will release on May 8th for PC & Mac. The DLC will be free.
The Perpetual Testing Initiative will allow players to create their own puzzles and share them. Created puzzles can be published onto the Steam Workshop where other players can rate them. Valve has also stated that, “Selected puzzles will automatically be downloaded and installed inside Portal 2.”
So far there’s no word on a release of this DLC for either the PS3 or Xbox 360.
Source: Press Release