LambStatus - Serverless status page system which enables you to build a status page with minimum effort and cost!
Pingdom - With website monitoring from Pingdom you will be the first to know when your website is down. No installation required. 30-day free trial.
cState - 🔥 Free & open source under MIT!
UptimeRobot - Free Website Uptime Monitoring
Cachet - Cachet is a free, open source status page for your API, service or company. Built with all of the features that you'd expect from a status page.
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring