It's a weird concept, traipsing around the Portal 2 universe without the famous portal gun - but you still get a weapon, just with different mechanics.
This new weapon is a Paint Gun that fires gel instead of portals. Below is a short description of the mod as seen on the Steam store page.
“Aperture Tag: The Paint Gun Initiative is a mod for Portal 2, inspired by TAG! The Power of Paint. The familiar Portal 2 gels are now contained within the Aperture Science Paint Gun Device and it’s your job to test it out! Featuring a new personality-core and an original story with 27 polished levels; the mod offers an exciting and fun experience in varied and interesting new locations throughout Aperture Science. Introducing gels as the core gameplay mechanic completely changes the way you solve puzzles, explore, and survive all the challenges thrown at you!”
The Aperture Tag mod, which was previously a free download, has been made from the ground up and boasts new puzzles, 27 new stages, a new character, new story, new voice acting and a nifty level editor, which can be used to create levels for single player and co-op games.
The co-op feature of the game is not fully working yet however, as noted by the developer on the game's Steam page.
"The current state of co-op is that it’s playable, and its fun, but it is not as polished as I would have wanted. There is bug which makes it so that sometimes your paint gun works and other times it wont work properly, and it seems to be completely random, so when playing Workshop co-op maps, you may need to click multiple times until you get your gel. I will keep on trying to solve this issue, but rest assured, the co-op area of the game is still playable.
If you are interested in playing Portal 2 without the support of Portal Gun, then do try out this mod, which is on 30% discount until 22 July.
Check out the trailer below or go buy the game at its Steam page.