I spent large chunks of my life on Citadel BBSes based in the Twin Cities during the '80s and early '90s. A *lot* of time (for good or ill).
I'm still friends with plenty of people I met on those BBSes, I've lost touch with others. I've got good memories and not-so-good memories (of course).
There's a Citadel webpage that contains some information. And I recently stumbled on this archive which has copies of a bunch of different variations on Citadel software.