alt Hacker NewsIt depends on the era.
Earlier: one PC per user, shared file system using a Novell network. Later: multitasking OS (Desqview, OS/2) or BBS software that natively supported multiple users (like MajorBBS.)
I ran a BBS on an Amiga for a while. The OS natively supported multitasking, but I only had one line. At least I could log in the same time as a user...
The older brother of a friend of mine in the 90s was the co-sysop of one of Sweden's largest "elite" BBSes at the time, Farout BBS. I got to tag along to the sysop's apartment once and see the setup, which was an Amiga 2000 with 3 active nodes and available serial ports for a total of 7 nodes, though the sysop hadn't gotten around to get more telephone lines wired to his apartment.