ServerSuit - ServerSuit is a browser based program that enables remote Linux administration, monitoring, website hosting, and server setup automation.
UptimeRobot - Free Website Uptime Monitoring
AppZero - AppZero is a monitoring and migration tool that allows users to keep track of different applications and servers in both simple and complex IT environments.
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
Ekran System - Ekran System is an enterprise-grade user monitoring software.
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.