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