Comment by ttkari

Back in 1980's the Finnish public broadcaster YLE used to broadcast Commodore 64 software in their radio show Silikoni. They actually have a recording the first such episode available online at https://yle.fi/a/20-108142 - of course, this is in Finnish.

It was not a very reliable method but it did work if you had good FM reception and a high quality tape deck. I guess it helps that the data rate is only 300 bits per second or so.