Hey all, neighborhood moderator WinstonSmith here. We’re starting a bit of a "Community Roundup" thing at TWP considering that people have begun to do wonderful things with the Alien Swarm SDK (interested? Check around for more info!). Most are singleplayer maps, but we have a multiplayer map in there too and a few neat tools people have thrown together. So, without further ado:

Singleplayer:
Synchronicity
Created by Omnicoder, Synchronicity is a well-rounded demonstration of many of Portal 2’s concepts, including the Discouragement Beam, Light Bridge, different gels, and Excursion Funnel. As usual, Omni is able to create intriguing puzzles in small spaces without becoming frustrating.

Sequential–Part 1
Created by Nightgunner5, the first part of Sequential is well-done. It contains puzzles utilizing many Portal 2 mechanics and has rather pretty lighting to boot. It concludes (for now) with a rather tough beam redirection puzzle.

Gravity Trials
Created by naitoookami, Gravity Trials explores the concept of (as you may have guessed) switching gravity. While not the most complex puzzles, it sets the stage for future use of gravity-oriented puzzles.

Multiplayer:
Colours Co-Op Part 1
Created by IanB, this short but satisfying map has a slightly different style than Portal 2. All the same, it looks fantastic and the creative voicework makes it a must-play.

Tools:
Crook’s Custom Maps to Extras App–Parses custom maps found in the Portal 2 maps folder and adds them to the extras.txt file, letting you launch them from the Extras Menu.
Nightgunner5’s Extras Patcher–Assists in adding maps to the Extras menu.
Haavapuo’s Extras Menu Patcher–Another tool to add maps to the Extras menu.
Magic94’s Map Loader/Starter–Another tool that copys maps to Portal 2’s folder and launches it.
Omnicoder’s Custom FGD–Use this to map for Portal 2. Updated version is in the description.

Enjoy!

(Note: as of right now I’m only taking released maps, not WIPs. Partly because I’m a bit pressed for time at the moment, I’ll probably look at them later.)