Datadog - See metrics from all of your apps, tools & services in one place with Datadog's cloud monitoring as a service solution. Try it for free.
Zenoss Core - Zenoss (Zenoss Core) is an open source application, server and network management platform based on...
Prometheus - An open-source systems monitoring and alerting toolkit.
LANState - LANState - Network Mapper and Device Monitor
Nagios - Complete monitoring and alerting for servers, switches, applications, and services
Zabbix - Track, record, alert and visualize performance and availability of IT resources