Siftables - The Smart Blocks

What are Siftables?

Siftables are cookie-sized computers with motion sensing, neighbor detection, graphical display, and wireless communication. They act in concert to form a single interface: users physically manipulate them - piling, grouping, sorting - to interact with digital information and media. Siftables provides a new platform on which to implement tangible, visual and mobile applications

To learn more - 

http://www.ted.com/talks/david_merrill_demos_siftables_the_smart_blocks.html

Personally, I think that the potential for mobile applications with the concept that they are presenting is huge!