WDT.io
NIXStats
Server Monitoring
Nodeping
mackerel.io
Platypus
Nubity
NetStairs
Zenoss Core
Nagios
Gitwin
LANState
System Center Operations Manager
Zabbix
Opsview Atom
Shinken
NIXStats - SaaS monitoring tool for window/linux servers and websites. Think up-time robot but with more features.
Nagios - Complete monitoring and alerting for servers, switches, applications, and services
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.
Gitwin - Enable your Windows system as a powerful and secure Git repository. Supports ssh, http(s) transports. Gitweb with highlighter and gravatar support available.
Nodeping - NodePing Server Monitoring and Web Site Monitoring. Simple but powerful Internet service monitoring.
LANState - LANState - Network Mapper and Device Monitor