I came across DCC (Digital Compact Cassettes) this month: https://en.wikipedia.org/wiki/Digital_Compact_Cassette. A digital cassette tape format with the players being backwards compatible with standard audio cassettes. Not massively surprising that I didn't remember them from the 90s, as they were about for roughly 4 years and lost to MiniDisc, which itself wasn't particularly successful. So many of the inventions of that era are a fascinating combination of mechanics and electronics.