This. Is. Awesome! Behold, the Gear Ring by Glen Liberman of Kinekt Design. It's available in a few standard ring sizes and in limited quantities:
The Gear Ring is made from high quality matte stainless steel. It features six micro-precision gears that turn in unison when the outer rims are spun (as can be seen in the video).
Hit play or go to the company's website: Link
I still want one, though.