Sonic After the Sequel is a fangame by FakeLeperd. The game is meant to detail the events after Sonic the Hedgehog 2, leading up to Sonic the Hedgehog 3. The game sees Sonic through new zones, with new sprites, enemies, and even powerups!
As of right now, the game itself is finished with development and is awaiting the completion of the OST. Like Sonic Before the Sequel, the soundtrack is a completely original creation, and like SBtS, has a lot of heart being put into it. The artists from last time have returned; Falk, Funk Fiction, Ristar, and KgZ. In addition to making more of a collaboration on their music this time around, we also have new artists for the soundtrack! Those artists are Mr. Lange, DJ Max-E, and Xiao'an Li.
Personally, I'm looking forward to the completed soundtrack more than anything. I never ended up finishing SBtS's actual game, but I listen to the soundtrack on a regular basis, and I suspect that's going to be the same case here. The game certainly looks interesting though, especially with those Kirby-inspired powerups. (What is it with Sonic fan-stuff and Kirby) Anyway, feel free to share your opinions!