Trackmate, originally uploaded by jean … 

Trackmate, originally uploaded by jeanbaptisteparis.

Trackmate is an open source initiative to create an inexpensive, do-it-yourself tangible tracking system. The Trackmate Tracker allows any computer to recognize tagged objects and their corresponding position, rotation, and color information when placed on a surface. Trackmate sends all object data via LusidOSC (a protocol layer for unique spatial input devices), allowing any LusidOSC-based application to work with the system..

Some articles about it in instructables, createdigitalmusic and make magazine.