Svsh provides a shell for already existing and running supervisors, specifically runit, daemontools, s6 and perp, which are all part of a "family" of similar supervisors. Svsh is external to them, it isn't a supervisor of its own, it just provides a better(?) interface to them.

I actually wrote it because, after switching from supervisord to perp, I was missing the shell provided with supervisord (supervisorctl).