Sixteen cubic robot pieces, plus 56 steel spheres, let you create a variety of electrical/ mechanical inventions that can respond to proximity or light.

The Cubelets Six kit ($150) contains 6 Cubelets for simple mobile and reactive Cubelet robots. Charging cable included.

The Cubelets Twenty Kit ($500) has 20 blocks and an assortment of Sense, Action, and Think blocks. It obviously offers much greater opportunities for experimentation. A "Brick Adapter" lets you pair Cubelets with Lego parts (note that there is no business relationship with Lego).