Earlier quoted context omitted.
For the init system, the most common predecessor was a combination of sysvnit and "initscripts" (a shell script for each daemon on your system). Writing the init scripts was simple for the most basic cases but quite complex for complete, bug free case coverage. A big appeal of systemd for packagers and sysadmins was the relative simplicity of unit files. Now we just have to fill out a simple boilerplate INI style fil…
It was not. There is strange false history that systemd replaced sysvinit, which occurred only on Debian, because Debian was the last major system to discard sysvinit. Gentoo had replaced sysvinit with OpenRC in 2006; Fedora and Ubuntu were using Upstart in 2005. systemd primarily replaced Upstart and systems that used Runit or OpenRC tended to have stayed with them. Frankness be, this false history seems to be craft…
I would add S6 to the list, as this would be the better challenger to systemd. That said, I use OpenRC daily on Alpine servers with little to complain about.