The Multi-Touch Ring Development Kit from Grahill INC. The ring encoder is mounted in a case complete with a standard USB lead to connect to a PC. Software is available via download
Up to 5 touch capacitive touchpad
Proximity sensor for device location and wake up
Optical encoder with 32 position detent
Integral pushbutton
Backlit with adjustable brightness settings
Any OS that supports USB HID can be used to get the raw data from the device