For a few weeks I ran a MUD over AX.25 for a couple of my friends.

Because on their own, MUDs aren't nerdy enough, amateur radio isn't nerdy enough, and indeed packet radio isn't nerdy enough.

Eventually we decided we'd had our fun and now I needed to the TNC for something else.

Ah, my grandfather was a ham (N4MDB) and he always tried to get me interested in it, but I had to tell him I preferred the internet (this was late 80's, so few people actually had internet). Later when I read Stevens networking books I learned there was a whole Hawaii-based packet radio (ALOHAnet) , and the UC campuses had intercampus microwave networking for a while as well. I actually still remember him telling me about bouncing radio waves off the atmosphere which seemed like magic to me at the time.