Minidiscs! We definitely used those a lot at university/various radio stations. At one point, one station had a stack of 'emergency' hour-long shows on them of a friend and I doing incredibly vague commentary between unremarkable songs. How often they got used, I'm not sure, but they were a thing.

I think I finally pitched the last few I had around, having no way to play them and no actual desire to listen to old projects/demos from the early-00's. But they were great for industry/student use. (The blank, re-recordable ones I mean. I only ever saw a handful of commercial releases and it's a little sad they didn't catch on, but they just came too soon to when full CD adoption was just finishing and nobody was quite ready to move on again.)