The Starpath Supercharger, pictured with its games above, was an expansion cartridge device used to play cassette-based games on the Atari 2600. Yeah, I didn't know about it until recently either. But I found out about it when I was researching Dragonstomper, the first, real RPG on a gaming console. Featuring a quest involving a dragon, money you can use to buy things and bribe guards, item shops, and other staples of the genre, Dragonstomper was too big for a normal Atari cartridge, and thus was on a peripheral no one ever bought. 

I never heard of it when I was a kid, or of the Supercharger. But I was aware of tape-based media, because we had a computer that used it. 

In 2005, Forbes Magazine listed Dragonstomper as one of the most impressive games made by a single person. The game is still praised for its cleverness, considering the system's limitations.