I thought this was truly fascinating: Dani Clode developed a "third thumb" that goes on the opposite side of your hand to your natural thumb. It is controlled remotely via your two big toes. It was tested on 600 people at an event and most were controlling it successfully in under one minute.Extraordinary. Here's two videos on it:
Clode's own site also has some fascinating non-third-thumb material.
Via Metafilter
