Students from Massachusetts Institute of Technology have designed and invented a new way to ride the T in Boston; 3D printed rings that are RFID enabled. They call it the Sesame Ring. This means that instead of digging around in your wallet or backpack for your subway card, it is right on your finger ready to be scanned to make the process smoother and more efficient. People 
will be able to load money onto the ring, just as you would your Charlie card, and just place the ring on the scanner to get through the doors onto the subway. The Sesame Ring is approved by the Massachusetts Bay Transportation Authority. Each ring is 3D printed and customizable to what you prefer for design.
You can read more on the Mashable website here.
(Picture from Mashable http://mashable.com/2013/08/27/sesame-ring/)