The Griffin PowerMate is an input device produced by Griffin Technology for computers equipped with USB ports. First released in 2001, it is a multifunction knob, which can be rotated or depressed. These actions can be programmed to invoke specific responses from a range of computer applications.
The PowerMate is also equipped with a blue LED on the underside, which can be programmed to flash, pulse, or remain illuminated at various intensities in response to input from the attached computer .
Griffin PowerMate Wikipedia
The PowerMate can be set up such that the clockwise/counter-clockwise rotation of the input device causes scrolling up and down of a web page in a web browser when it is in focus on the desktop, or the system audio volume when it is not. The status LED on the underside of the PowerMate could be set up as an indicator of resource usage, i.e. CPU usage, when the input device is not in use, and when in use the LED could be set to indicate volume level by LED brightness.
The configuration software allows for custom configuration for each software application. A video editing program can use the PowerMate to scroll through the timeline. Or it can be configured to scroll through your browser page history and push to refresh. It would also work well for breakout-style games. By adding "Key Press" actions, PowerMate can be configured to perform any particular software function for which there is a "send key" command - i.e., a keyboard shortcut of one or more keys. By setting "Actions" (e.g., "Key Press") for "Triggers" (for example, "Long Press" or "Rotate Right"), a user can use PowerMate in place of the keyboard for any command.
The Griffin PowerMate is officially supported on Mac OS X, Windows XP and Vista. The software also works under Windows 7 and 8 but crashes occasionally. There are Linux drivers but they are unofficial.