The Powershell is a combination controller extension and battery pack designed to turn a touch-screen iPhone into a button-mashing game pad.
It is a very long device, almost doubling the length of the cellphone when it is installed, but that added length makes for greater control with both hands. The Powershell is built by Logitech, an Irish manufacturer with a long history developing computer mice and other robust input devices.
In addition to providing a better control scheme for most games, the Powershell also increases play time between charging, offering a sizable backup battery. This makes the increased size of the device somewhat more palatable, as users realize they've got more than one reason to keep the cellphone too big to fit in their pocket.