ARB BBS v7.60 by Arthur Brock (1988) - I've never run ARB before, but I know at least one of our visitors is a huge fan of this BBS software for the Commodore 64.  ARB supports the 1764 RAM expander and the 1581 floppy drive, so it must have been one of the most up-to-date BBSes for it's time.

From what I understand, there is a bit newer version 7.62 which I'd like to locate if anyone can help out.