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.
Hyperping - Cheap uptime and performance monitoring with detailed reporting and flexible alerting
Oh Dear! - Website monitoring, without the hassle
Freshworks - Delight your customers, from wherever you are
updown.io - updown.io is a HTTP(S)/TCP/ICMP monitoring service which checks periodically the URL you want and reports back any anomaly.
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.