Pingdom - With website monitoring from Pingdom you will be the first to know when your website is down. No installation required. 30-day free trial.
PagerDuty - Cloud based monitoring service
UptimeRobot - Free Website Uptime Monitoring
OpsGenie - Alerting and On-Call Management for Dev&Ops Teams
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.
Squadcast - Automate incident response, reduce downtime and enhance your tech teams’ delivery with a unified platform.