I worked for Exec PC internet which evolved from the BBS which was the largest in the US afaik. It ran on somewhat custom PCs where there were I think four nodes per board on bread racks. No cases. Custom software. That BBS was over 250 lines at one point. I remember hearing stories the room with the modems, a lot of Couriers near the end, was so hot they would have to replace dead ones every week.

ExecPC had shelves of Couriers and at some point they were just bare modem cards not in indiviual cases. It was impressive to see.