Rave Alert - Rave Alert is a multi-modal emergency notification system used by state and local governments, colleges, hospitals and universities.
Zabbix - Track, record, alert and visualize performance and availability of IT resources
DialMyCalls - The easy to use mass and emergency notification platform. Send a phone call, text message or e-mail to your entire list of people in seconds.
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.
Call-Em-All - Call or send messages to friends and family members as well as other people who are online. The app allows you to create a message and send it out to multiple devices and pages.
Nagios - Complete monitoring and alerting for servers, switches, applications, and services