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.
AirBrake - Airbrake is the leading exception reporting service, currently providing error tracking.
TrackJS - JavaScript Error Tracking for Modern Web Applications
Instabug - The top apps in the world rely on Instabug for beta testing, user engagement and crash reporting.
Raygun - Raygun gives developers meaningful insights into problems affecting their applications. Discover issues - Understand the problem - Fix things faster.
elmah.io - The coolest cloud based error management system for .NET web applications. Based on the de-facto standard error component ELMAH, logging errors from your webserver have never been this easy. Full-text search, notifications, API and much more.