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.
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.
RootCause - Record, Replay and Reproduce JavaScript Errors
Instabug - The top apps in the world rely on Instabug for beta testing, user engagement and crash reporting.
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.