dbus-daemon works on BSDs too. There as a Linux-specific implementation of D-Bus called "dbus-broker", but that's an implementation of D-Bus, and Cockpit doesn't care about that at all.
It too, like Cockpit here (as shown at https://news.ycombinator.com/item?id=16448768), talks directly to the idiosyncratic systemd process #1 API (rather than, say, using the "service" command to start services on demand).
* https://github.com/bus1/dbus-broker/blob/07e43501e418c8066c7...