Sonic the Hedgehog

Sonic the Hedgehog is an unlicensed fan-made demo of a pretty well-made Sonic engine for DOS. This is not emulated; it's built-from-scratch using the DIV Studio game making software. The game uses graphics that match the Genesis game, although the sound quality is not great. It includes two full levels, with a boss stage after each one. It plays well enough, although the controls could be a little more responsive. Nonetheless it's an impressive achievement, with parallax scrolling and generally just feeling like a Sonic game.