Though you may have completely forgotten it existed, the MiniDisc was actually pretty revolutionary when it was introduced in 1992. It used magneto-optical technology and behaved a little like a hard drive crossed with a miniature 6-cm CD. It also hit the market long before user-recordable CD  technology did. But its innovative potential was stymied thanks to Sony's usual trick of creating proprietary formats  and strict Digital Rights Management, and the MiniDisc was never as popular as CDs. It was also quickly superseded by many different technologies.
I listened to MiniDisc recordings many times. But do you remember this tiny disc?
[Image: Flickr user raeallen ]