Siftables.

The Siftables project is an example of how TUI and fluid interface (FI) interaction can be combined.
Siftables is the work of David Merrill and Pattie Maes, in collaboration with Jeevan Kalanithi.
"Siftables aims to enable people to interact with information and media in physical, natural ways that approach interactions with physical objects in our everyday lives. As an interaction platform, Siftables applies technology and methodology from wireless sensor networks to tangible user interfaces. Siftables are independent, compact devices with sensing, graphical display, and wireless communication capabilities. They can be physically manipulated as a group to interact with digital information and media. Siftables can be used to implement any number of gestural interaction languages and HCI applications....Siftables can sense their neighbors, allowing applications to utilize topological arrangement..No special sensing surface or cameras are needed."

Siftables Music Sequencer from Jeevan Kalanithi on Vimeo.
More about Siftables:
Siftables: Toward Sensor Network User Interfaces (pdf)