Zabbix - Track, record, alert and visualize performance and availability of IT resources
PagerDuty - Cloud based monitoring service
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.
VictorOps - We make on-call suck less & help teams to solve problems faster.
Nagios - Complete monitoring and alerting for servers, switches, applications, and services
LogicMonitor - LogicMonitor is the SaaS performance monitoring platform for the world's best IT teams. Deploy Fast, Monitor More, Improve Ops.