Uptime Kuma
Uptime Kuma is a self-hosted, open source, fancy uptime monitoring and alerting system. It can monitor HTTP, HTTP with keyword, TCP, Ping, and DNS systems.
Uptime Kuma is an easy way to know if your systems are up and running. You can even add your favorite Internet sites (i.e., Facebook, Amazon, Twitter, etc.) if you want to be sure they are working. I use Uptime Kuma primarily for my home LAN components and any websites/applications I host from home.
Uptime Kuma even permits me to provide status pages for my users so they can know at a glance if any of my services are down or under maintenance.