Zow! I had no idea FirstClass was a BBS server. I had a Customer in the early 2000's who was using a FirstClass server on a LAN for email, calendaring, and collaboration. It struck me as a really neat piece of software, albeit I would have preferred a web interface to the thick Win32 client. It was very well thought-out software, albeit I didn't have to sysadmin the thing (so I don't know what the back-end was like in terms of reliability, backup/restore, fault tolerance, etc).

I'm off to go down a rabbit hole re: the FirstClass software.