Free Music Software: The D-Touch Sequencer and D-Touch Drum Machine are free downloadable apps that let you experiment with tangible sequencing:

The audio d-touch interactive surface consists of a simple printed piece of paper. The movable physical objects are marked using labels, also printed on normal paper. The computer observes the blocks and the paper through a low cost web-cam, and thanks to the d-touch marker recognition algorithm it can localize them precisely.

The information about the position and orientation of each block is used to control a digital audio synthesis process. The system was designed to be extremely low cost, robust and easy to set up, which makes it possible to fully and freely release it for download.

More info and download are available at the D-touch site.  See below for performance demos.