I'm working on my number station article today for the next zine. I do my first drafts in emacs still and then I narrate them.
If you want to be on the tape, submissions are always open! I think each tape so far has more contributors than the last.
The audio can be pretty much anything but definitely the more experimental is best suited for a cassette medium.
As one tapehead put it, "I'd rather listen to a backyard production of star wars recorded to cassette than studio music."
This issue has so far: a radio drama, 2 spoken word pieces, generated music, a cool sstv submission, and working on some poetry submissions.
If you need inspiration, listen to the Tellus audio magazine from the 80s: https://www.ubu.com/sound/tellus_5-6.html