PagerDuty - Cloud based monitoring service

Exceptionless - Don't let your users walk away in frustration.

OpsGenie - Alerting and On-Call Management for Dev&Ops Teams

Sentry.io - From error tracking to performance monitoring, developers can see what actually matters, solve quicker, and learn continuously about their applications - from the frontend to the backend.

xMatters - xMatters transforms event data into intelligent communication IT teams, avoiding outages and disruptions

RoRvsWild - All-in-one monitoring for Ruby on Rails applications. Track performances & errors for requests & background jobs.