NIXStats - SaaS monitoring tool for window/linux servers and websites. Think up-time robot but with more features.
SevOne - SevOne provides network managers with monitoring, troubleshooting, and performance reporting capabilities.
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.
The Dude - MikroTik is a Latvian company which was founded in 1996 to develop routers and wireless ISP systems. MikroTik now provides hardware and software for Internet connectivity in most of the countries around the world.
mackerel.io - mackerel.io is a server and application performance monitoring platform.
Obkio - Simple Network Monitoring and Network Troubleshooting software to empower users to identify and troubleshoot network & application slowdown from the end-user perspective.