Filesystem:/Applications/Diagnostics.app

This (hidden) application is usually used at the Genius Bar in Apple Stores. It sends diagnostic data of a device to a Genius' iPad/Mac throughout the website https://diagnostics.apple.com. It is present on iOS 8.3+. Older devices use /Applications/iOS Diagnostics.app instead.

The application can be opened by typing "diagnostics://" in Safari or, once a diagnostic ticket has been created, from Settings > Privacy > Diagnostics and Usage.