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.
One Call Now - One Call Now's message notification delivers automated phone calls, SMS text messages and emails within moments to any group.
AppDynamics - Get real-time insight from your apps using Application Performance Management—how they’re being used, how they’re performing, where they need help.
OpsGenie - Alerting and On-Call Management for Dev&Ops Teams
Zabbix - Track, record, alert and visualize performance and availability of IT resources