It's finally here! Valve's have announced that the free Portal 2 update 'Perpetual Testing Initiative' is now available for download. Did we mention it's, uh, free? Yep! If you already own Portal 2, you now own this.
Perpetual Testing Initiative is available for both PC and Mac, and lets players "easily create, share and play Portal 2 puzzles". The DLC pack sports a simplified Puzzle Maker which makes the creation of Portal 2 maps that much easier.
The Puzzle Maker can also directly publish maps to Valve's Steam Workshop, where everyone else can browse, vote on, and select to play them.