BeBS is the first BBS software available for BeOS.
BeBS is a Citadel-86 clone, rewritten from scratch in C++ to take advantage of all that Be has to offer. It supports a (theoretically) unlimited number of simultaneous connections, and is one of the only online citadel clones I know of that supports door games.
Administration is simple--most common tasks can be handled from the console. Otherwise, all users/posts/rooms are directories or files, and are easily moved about or deleted as needed.