NIXStats - SaaS monitoring tool for window/linux servers and websites. Think up-time robot but with more features.
mackerel.io - mackerel.io is a server and application performance monitoring platform.
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.
BizTalk360 - BizTalk360 is a web based production support/monitoring tool for Microsoft BizTalk Server.
Nubity - Nubity provides SaaS-based, centralised public and private cloud manager platform to manage and monitor servers.
SolarWinds System Management - Performance monitoring and management for applications, Websites, servers, storage arrays and virtual infrastructure.