> Similarly, the claim that cron is only just now being reinvented from scratch looks rather ill-informed given the existence of tools such as Uwe Ohse's uschedule and the multiple "cron" tools, many of which reinvent the design in significant ways (Bruce Guenter's split of scheduling, spooling, and updating into separate services being a notable example); and given the fact that Paul Vixie's "original" PD Cron was actually itself a from-scratch clone.

My response to both of these are, can you point out any of them that are part of a monolithic system that replaces the traditional PID 0?

Or are you talking about people reinventing small parts of the general system? Yes. UNIX allows people to swap out software for other software. In the original use-cases though, the editor(1), cron(1), and nice(1) were at no point conjoined with the boot menu system, or PID 0.

Indeed, there is a fundamental choice between someone building a replacement for one small part of the general system, to make their life easier, and building a replacement for the entire init system.