Sonic 2 Delta
From Sonic Retro
Sonic 2 Delta is an amazing hack by Esrael Neto, which features restored deleted levels such as Wood Zone, Hidden Palace Zone, the desert level and the winter level. It also features various imports of art and original additions to the game, such as a total ring counter.
You can find out more about Sonic 2 Delta if you can read Portuguese by visiting: Esrael Sonic Hacking H.P.