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.
Sorry App - Turn outages into opportunities
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
StatusPage Generator - Host your status page on GitHub
Better Uptime - We call you when your website goes down
Project Pulse - Project status pages communicate progress for you