Systemd has become quite popular among Linux distros, but it's not universal; plus Linux isn't the only Unix system around; and there's more to operating system

Systemd has become quite popular among Linux distros, but it's not universal; plus Linux isn't the only Unix system around; and there's more to operating systems than just Unix. It's also not just a matter of time before everyone switches over, since there's been backlash against systemd and competing projects have either started up, or gained more momentum (except for upstart, obviously!). One of those alternatives is the "dmd" init system, which seems to have been around for a while but has recently been rebranded as "GNU Shepherd". Shepherd follows the "do one thing well" philosophy, so it only manages daemons. If shepherd users (e.g. GuixSD) want to run scheduled commands, they'll need another program to do that (i.e. a cron daemon), and GNU Mcron looks like a sensible choice since all of these things are configured using Guile Scheme. As a side rant: I dislike your use of the term "legacy" for something which is actively maintained and gaining users. Usually "legacy" refers to something which is either abandoned, or where the maintainers recommend against adopting it (e.g. "that's our legacy API, use this other one instead"). I think the word "traditional" would work, when talking about cron in general; although Mcron in particular doen't look like a particularly traditional cron (since its selling point is using Scheme for config!)