PagerDuty - Cloud based monitoring service
Rave Alert - Rave Alert is a multi-modal emergency notification system used by state and local governments, colleges, hospitals and universities.
OpsGenie - Alerting and On-Call Management for Dev&Ops Teams
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.
Squadcast - Automate incident response, reduce downtime and enhance your tech teams’ delivery with a unified platform.
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.