Trackmate is an open source initiative to create an inexpensive, do-it-yourself tangible tracking system. Using the project's Tracker software, any computer can recognize tagged objects and their corresponding position, rotation, and color information when placed on the imaging surface.
Using a system like the one shown here, you can track physical objects on a surface and use them to control and manipulate spatial applications on your computer. Since objects are each uniquely tagged, they can easily be mapped to particular actions, information, or relationships. See the LusidOSC project for more details about spatial applications.