Sega's 16-bit console, home to a good range of action games, most of them being arcade ports. And of course that sound chip. It also has lots of hardware variations and add-ons, such as the Mega-CD, 32x, Wondermega, and so on.
The 32X is a bulbous mushroom doo-dad intended as a life support device for the Megadrive / gap-bridger till the Saturn launch. It requires two proprietary cables to hook up to a Model 1, and one cable and a plastic spacer for a Model 2. It's sold less than half a million units and is generally hated by everyone today, usually only warranting mention for Chaotix. Many of the games for it were barely upgraded ports of Megadrive titles, or re-releases of Mega CD FMV games that used the extra hardware for better video quality. However, it remains my favorite unpopular console. There are a handful of highly experimental and interesting polygonal games, and arguably the best versions of some AM/2 arcade ports. There were scrapped plans to release it as a standalone console, the Neptune.
—Sniper Honeyviper (with edits)