These answers are provided by our Community. If you find them useful, show some love by clicking the heart. If you run into issues leave a comment, or add your own answer to help others.
@mosaic - If you’re looking for something free, but pretty reliable, I would recommend checking out UptimeRobot. You can setup 50 monitors for free and checks will be performed every 5 minutes. This is, IMO, more than enough for any basic website that isn’t hosting what I would refer to as “critical” content.
On the commercial side, and as a more reliable / feature rich alternative, I would recommend NewRelic and their line of services (though it does cost and it’s not cheap).
From GPU-powered inference and Kubernetes to managed databases and storage, get everything you need to build, scale, and deploy intelligent applications.