NIXStats - SaaS monitoring tool for window/linux servers and websites. Think up-time robot but with more features.
Platypus - Realtime server monitoring and reporting
Server Monitoring - A server monitor is a tool that monitors your server and website on close intervals and reports to you if it's inaccessible.
Nodeping - NodePing Server Monitoring and Web Site Monitoring. Simple but powerful Internet service monitoring.
Monitornator - Server monitoring made simple
Observu - Observu offers website, server and API monitoring solutions.