I recently discovered rkt, a competitor container runtime to Docker. It seems like rkt does not need a daemon. For me, rkt is like running any other command and it works easily with systemd (or other init systems).
This makes me wonder about the utility of Docker's daemon.
Why does Docker need a daemon ? What does the daemon provide that would not be possible without it ? Is its only goal to remove the need for an init system like systemd (as can be seen in the Rancher OS) ?