AirBrake - Airbrake is the leading exception reporting service, currently providing error tracking.
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.
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.
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.
HoneyBadger - Exception, uptime, and performance monitoring for Ruby.
Zabbix - Track, record, alert and visualize performance and availability of IT resources