#hall-sensor

It's a little like a Meccano/Erector set that can "interact" with things on a tablet. Not only can the shape of the GaussBricks object be detected by and influence the animation on screen, actuator bricks can be used to make the GB object change shape in response to the "impacts" of on-screen objects with the shape placed on top of the screen. Wild!

And they've provided information on how to make your own bricks, and the sensor board schematics are public, or you can have one made.

I'm not sure how useful the bricks themselves are, other than for fun and as a prototyping tool, but I can see this as an alternative to cameras for detecting objects placed on a screen in a TUI.