The example uses Dead Man's Snitch, Healthchecks.io is my preference and their plans offer more for less. Both offer code on Github for examination.
https://deadmanssnitch.com/plans vs. https://healthchecks.io/pricing/
Is there anything self hosted in this space?
Yes, Healthchecks is open-source and can be self-hosted
https://github.com/healthchecks/healthchecks