Sonic 3 A.I.R. (short for Sonic 3 Angel Island Revisited) is a fan-made widescreen-capable remaster of Sonic 3 & Knuckles. The game needs an original uncompressed ROM of the original game (which can be obtained legally if you have the original Sonic 3 & Knuckles installed via Steam (under SEGA Mega Drive & Genesis Classics), because this tool extracts a lot of information from the ROM.
The game fully supports controllers, and includes achievements, with some rewards unlocked depending on the number of achievements unlocked.