Fabric.io is a platform that provides many services for building better apps, to grow performance and look into the insight of user and business behavior.
The most useful feature provided by Fabric.io is Crashlytics, this is an error reporting tool which immediately reports issues in an application like warning, error or fatal crashes in an application. It really helps in making applications bug free more smooth for better user experience. You can read more about services and feature on their official site.