Most uptime monitors either give you 50 free monitors with no alerts, charge $20+/mo for basics features.
Upwatch is the middle ground. Free tier that actually works. No feature walls on the stuff that matters.
What's different:
HTTP, TCP, and Ping monitoring - Not just website checks. Monitor databases, mail servers, game servers, or anything with a port or IP.
Body matching - POST or PUT a JSON payload to your health endpoint and validate the response body.