Boards
Around the same time CDs were created I met someone with a double-sided vinyl player.
You know, it had two styluses and the record was held vertically so it could play both sides, one after the other.
I have no idea how much such an amazing invention cost but I was only about 8 I guess so even if I'd been told then the effects of 26 years of inflation would likely render the price meaningless.
Still, that's some major cool shit, yeah?