Sonic 3 Complete is a hack of Sonic 3 & Knuckles which aims to provide a much improved variant of the original game, with many new options and features, without straying from the original levels or gameplay. The inclusion of separate modes for Sonic 3, Sonic & Knuckles and Blue Sphere also make this a close cousin of the PC compilation Sonic & Knuckles Collection.
More info: http://info.sonicretro.org/Sonic_3_Complete
Note: This may run into freeze issues on the MK1 Mega Drive. It's recommended to play it on the MK2 Mega Drive.