Sonic 3: Angel Island Revisited (or Sonic 3 A.I.R. for short) is a mod... remake... thing of Sonic the Hedgehog 3. It takes the Steam version of Sonic 3 and overhauls it using an external .exe, adding 16:9 support, Achievements (with unlockables attached to them, a la the Mania Medallions), options for both emulated and remastered soundtracks, level design tweaks, new control options (Tails can drop out of his flight into ball form), a Time Attack mode, and much, much more.
Essentially, it's the Taxman version of Sonic 3 we've been waiting for, and the full game released today! I can't believe how quickly the remake's creator, Eukaryot, managed to get it all together - the full Sonic 3 & Knuckles experience is here, from Angel Island all the way to the Doomsday Zone, now in 16:9, 60fps, with smooth Mania style rotations and all!
I've yet to play through the game in full, but this is a seriously impressive effort. I'm not sure to what extent we'll be seeing updates (I'd love the ability to play through the game with the prototype level order), but huge props to Eukaryot.