The Sonic & Knuckles Collection is actually a release of the following games ported from the Sega Genesis / Mega Drive to Windows:
- Sonic the Hedgehog 3
- Sonic & Knuckles
- Sonic 3 & Knuckles
It has been done by the Sonic Team and published by SEGA in 1997.
In this video, you can see the demo version of Sonic 3 & Knuckles. This game has been released independently on Steam in 2011.