Inferno in iOS 8 is a diagnostic utility used for testing in the factories for certain logs and has not been seen since the iPhone 4
All tests are performed via a usbmux interface. During that time the iPhone displays a green colored screen of logs that were collected and it either passes or fails.
There is an option to shutdown the device in the newer versions of Inferno, and Inferno displays the device identifier, the time, and the battery at the top at the status bar. At the bottom, Inferno shows the build number of the device in testing, the sequence of the testing, and gives an option to shutdown towards the bottom of the Inferno Utility
This version of Inferno has been seen first on the iPhone 5s, followed by the iPhone 6 and the iPad Mini 2