Game Gear:Master System Games on Game Gear

Game Gear cartridges can't be played on a Sega Master System or Genesis, but you can get a converter to play SMS games on your Game Gear.

Many different companies made SMS-to-GG adapters and most were licensed by Sega. They all worked well with one exception: The Nuby Converter (the right-most adapter in the picture) is the only one that works with the Majesco Game Gear, as well as the original Sega Game Gear. Although the adapters play all of the cartridge-based SMS games, they don't support 3D games or light gun games. Also, the Game Gear will not output FM audio from the SMS games, just the standard audio.

While this was a neat adapter to have back in the 90's, the Game Gear's original screen looks significantly worse than playing the game on a TV using a real Master System. Also, when you play an SMS game, the Game Gear shrinks the resolution and aspect ratio to fit it's screen. Here's an example of an SMS game being played on a Game Gear (left) and on an RGB monitor, just to show how bad it looks: