Nagios - Complete monitoring and alerting for servers, switches, applications, and services
Zenoss Core - Zenoss (Zenoss Core) is an open source application, server and network management platform based on...
Zabbix - Track, record, alert and visualize performance and availability of IT resources
System Center Operations Manager - System Center Operations Manager 2012 R2 uniquely enables customers to reduce the cost of data...
Opsview Atom - Monitor everything. Integrate anything. Scale anywhere.
Shinken - Nagios compatible monitoring framework, written in Python