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.
TrackJS JavaScript Error Logging - JavaScript Error Monitoring from TrackJS gives you context about what's happening in your end-users' browsers.
Dynatrace - Cloud-based quality testing, performance monitoring and analytics for mobile apps and websites. Get started with Keynote today!
Rollbar - Rollbar collects errors that happen in your application, notifies you, and analyzes them so you can debug and fix them. Ruby, Python, PHP, Node.js, JavaScript, and Flash libraries available.
Zabbix - Track, record, alert and visualize performance and availability of IT resources
CatchJS - Unbloated, yet feature rich. CatchJS provides JavaScript Error Tracking the way it should be.