Fedora was one of those two systems, using upstart since Fedora 9. If you are going to participate in a systemd discussion, you should know what you are talking about, lest you once again (as indeed you are) promote the There Is Only System 5 init And systemd fallacy. Read the Uselessd Guy's articles already pointed to. Read the Debian Hoo-Hah where there were four choices. Read Lennart Poettering's own explanation, widely published a couple of years ago now, of how upstart was the motivator.