Sonic Hex Adventure is a fan-made game for the Sega Genesis, likely inspired by the original Sonic games. It probably features new levels, zones, and possibly a new storyline, while keeping true to the classic 2D side-scrolling platforming of the series.  The name suggests a focus on adventure elements and potentially a unique level design.   As an independent project, it's not connected to Sega's official development team; its history is part of the broader landscape of fan-made Sonic content. 

Sonic Hex Adventure

Sonic Generations 2 