From Sonic Retro

This Sonic the Hedgehog CD prototype has many differences over the final game, such as this cluttered title screen.

On rare occasions, incomplete versions of Sonic the Hedgehog games find their way to the general public. As these copies differ from their final counterparts, they can often provide an insight into the original vision of the game, before deadlines or technical or design restrictions led the development team down a different path.

This category covers prototype versions and release candidates of Sonic games made available to the public, both those which made it to retail, and those which did not.