Suprvise is a real-time health monitoring and errors tracking dashboard.
WebGazer - Monitor your website's availability with WebGazer, review its performance and get instant notifications when your website goes down. No installation required and free plan available.
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.
Monitority - Simple website monitoring service (sms/email alerts)
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
Hyperping - Cheap uptime and performance monitoring with detailed reporting and flexible alerting
Better Uptime - We call you when your website goes down