Mod DB now offers THE CORE, a custom campaign for Portal 2, Valve's first person puzzle/platformer. Apparently some "fiddling" was required to get this working after the release of the new co-op DLC for the game, but it is now ready to roll. Here's word on what it offers: "THE CORE is a custom campaign for Portal 2 with a new testing approach called "fake coop". You will always be required to manipulate a cube ore a sphere trough the levels in order to complete them. In addition to 6 maps with new puzzles, the campaign contains additional GLaDOS lines as well as new music, madia and lines for the companion sphere you'll be working with..." Thanks Ant.