Sonic 1 Definitive

Sonic 1 Definitive is a hack named by RadiantNexus Team, which seeks to reimagine Sonic 1 by rearranging levels, remixing music, adding features from future games, and reading scrapped ideas in new and interesting ways.

Major features:

3 acts of reimagined level design, including one act that has yet to be fully reimagined in any other hack.

A miniboss.

Massive art overhaul all over the place.

Music made by ProjectFM and MechaKnuckles.

Menus!

A custom splash screen.

There's been massive engine overhauls as well, including the Sonic 3 level layout format for massive levels, and the Sonic 3 object manager to go alongside this.