Sonic 1: South Island Expedition

Sonic the Hedgehog: South Island Expedition, formerly known as Sonic 1 Definitive, is an extensive in-progress overhaul ROM hack of Sonic the Hedgehog developed by RadiantNexus Team. It is a re-imagining of the first game that aims to rework the entire game through rearranged Zones, whilst also implementing elements seen in future installments, pre-release material, the 8-bit game, and further sources. Among the changes is a revamped art style, redone music, additional cutscenes, and others. The current version consists of Green Hill Zone and previews of Bridge Zone and Marble Zone. Playable though unfinished teasers of Spring Yard Zone Act 1 and Bridge Zone Act 2 can also be unlocked through the Extras menu following completion of the main available Zones.

Source: TheGamesDB