There is a lot of system services other than those provided by systemd on Linux that provide a DBus API - Network Manager, firewalld, storaged, sssd, packagekit

There is a lot of system services other than those provided by systemd on Linux that provide a DBus API - Network Manager, firewalld, storaged, sssd, packagekit, even the Anaconda installer. This can be at least partially due to DBus API being a pre-condition for making the given service configurable via the popular Cockpit web management interface.