Show HN: Caduceus: Be notified by email when your cronjobs don't run

I use something similar, based upon JSON submissions to HTTP end-points. Here is a brief overview of how you'd use it:

https://github.com/skx/purppura/blob/master/ALERTS.md

My particular project does more, but this style of "expect an update, raise if it doesn't arrive" is very natural and useful - a simpler alternative based just on that idea is nanny:

https://github.com/lunemec/nanny/

But I guess there are a lot of these packages out there, and a bunch of commercial SaaS implementations too.