I remember that well. We used DESQView to run our BBS as well. It was only a single line system, but DESQView let us do other things on the computer without taking down the board.
Has anyone played with TriDOS? https://github.com/prokushev/tridos - it doesn’t look nearly as featured, but has the advantage of being open-source and I thought might be interesting for a project I have in mind.