There were a collection of simpler boards used by pirate sites in the 80s, but community wise, I felt C-Net 128 was the most advanced BBS.
I spent about a year myself writing a modular BBS in assembly code to try and beat it, including a ram disk, multitasking with windowing system for sysops, federation and fast search indexing, but quit to move to Amiga in 1989.
BBS software was really the the Web 0.1 of its day and a very dynamic and fascinating field to watch develop.
I still have a fondness and warm feeling when I see an acoustic coupler or Vic Modem and the old Bell phones where you dialed manually and then disconnected the handset and quickly plugged it into the modem. Love watching Wargames because of this.