Built by a hardcore team, Crashlytics is an elegant solution to a big data problem. The most powerful, yet lightest weight crash reporting solution, they find the needle in the haystack, even the exact line of code that your app crashed on. Crashlytics is now part of Firebase.
Rollbar is a full-stack error monitoring platform for web and mobile applications. Rollbar help developers find and fix bugs fast. Built by developers for developers. Support for all languages, including - Javascript, Ruby, Python, PHP, Node, Golang, Flash, Android, iOS, more.
Sentry is an event logging platform primarily focused on capturing and aggregating exceptions. Sentry was originally conceived at DISQUS in early 2010 to solve exception logging within a Django application. Since then it has grown to support many popular languages and platforms, including Python, PHP, Java, Ruby, Node.js, and even JavaScript.