Statsignal - Statsignal is a simple and cost-effective way to monitor your website or server and publish a status page of your system.
OnlineOrNot - Uptime monitoring for software teams (even teams of one).
Site monitoring - Free open-source website monitoring software, easy to set up and use for monitoring web sites.
UptimeRobot - Free Website Uptime Monitoring
Uptime Kuma - A fancy self-hosted monitoring tool.
WebmasterSidekick - It is an All-In-One Site Monitoring & SEO Tool that Reports site Performance, Monitoring Key...