/Applications/iOS Diagnostics.app

This (hidden) application is an iOS version of an internal Apple OS X application named "Behavior Scan", used at the Genius Bar to detect and test different aspects of the device. The iOS version was added so that users could be better helped over the phone instead of making them come in to an Apple Store for support.

It sends data about the device to https://iosdiags.apple.com/MR3Server/MR3Post. The URL schema that it utilizes is diags://<ticket number>, where <ticket number> is the support ticket number given to them by Apple over the phone to allow them to send their device's data over to Apple.

Localization strings

Extracting its English localization strings yields these:

/* Privacy Information */
"By clicking “Send to Apple” you agree that Apple may periodically collect diagnostic data from this device, including the device serial number, device name and daily count of call attempts. This data will be used to troubleshoot issues with your device and to improve our products and services. For information on Apple’s Privacy Policy, see <a href=\"http://www.apple.com/legal/privacy\">http://www.apple.com/legal/privacy</a>." = "By clicking “Send to Apple” you agree that Apple may periodically collect diagnostic data from this device, including the device serial number, device name and daily count of call attempts. This data will be used to troubleshoot issues with your device and to improve our products and services. For information on Apple’s Privacy Policy, see <a href=\"http://www.apple.com/legal/privacy\">http://www.apple.com/legal/privacy</a>.";

/* Cancel */
"Cancel" = "Cancel";

/* Done */
"Done" = "Done";

/* App Title */
"iOS Diagnostics" = "iOS Diagnostics";

/* Last Sent: */
"Last Sent:" = "Last Sent:";

/* Never */
"Never" = "Never";

/* Next */
"Next" = "Next";

/* OK */
"OK" = "OK";

/* Send to Apple */
"Send to Apple" = "Send to Apple";

/* Sending to Apple... */
"Sending to Apple..." = "Sending to Apple...";

/* Ticket number is not valid error message */
"The ticket number was not found. Verify the number and try again." = "The ticket number was not found. Verify the number and try again.";

/* Submission error message */
"There was an issue with your submission. Please make sure you are connected to the internet and try again." = "There was an issue with your submission. Please make sure you are connected to the internet and try again.";

/* Ticket Number Placeholder */
"Ticket Number" = "Ticket Number";

/* Ticket Number: */
"Ticket Number:" = "Ticket Number:";

/* Ticket validation server is unavailable error message */
"Ticket validation has failed. Please make sure you are connected to the internet and try again." = "Ticket validation has failed. Please make sure you are connected to the internet and try again.";

/* Enter Ticket Number */
"To receive support services, enter the ticket number you were given." = "To receive support services, enter the ticket number you were given.";

/* Submission success message */
"Your information has been received by Apple." = "Your information has been received by Apple.";

Reference

Analysis on MacRumors forums