* http://cockpit-project.org/guide/latest/feature-systemd.html
It should of course be obvious that Cockpit does explicitly deal with systemd. Desktop Bus is a transport layer, and the important thing about it is what DBus servers are on the other side of the broker are being talked to. In the case of Cockpit they are things like systemd's own idiosyncratic API for process #1 ...
* https://github.com/cockpit-project/cockpit/blob/0dd4ee7bac14...
... systemd's hostnamed server ...
* https://github.com/cockpit-project/cockpit/blob/0dd4ee7bac14...
* https://www.freedesktop.org/wiki/Software/systemd/hostnamed/
... and systemd's timedated server.
* https://github.com/cockpit-project/cockpit/blob/dbd7f3a8487a...
* https://www.freedesktop.org/wiki/Software/systemd/timedated/
Cockpit also hardwires use of systemd's journalctl program.
* http://cockpit-project.org/guide/latest/feature-journal.html
* https://github.com/cockpit-project/cockpit/blob/0dd4ee7bac14...