Cubelets are blocks that fit together using magnets. They don’t require programming, and are suitable for the youngest children, though everyone finds them fascinating. Each block has a different function and the blocks you choose and the way they are connected determines how the robot behaves. Each Cubelets kit includes two black sensor blocks (light and distance), two clear action blocks (a drive block with rollers and a light), and a dark grey power block. The bright green block is a connector block that is useful for building larger robots, and the light blue block is a Bluetooth block for communicating with an iPad or Android device.

Cubelets are made by Modular Robotics in the USA, and they have produced a brilliant little video that shows that building a robot with Cubelets is faster than making a sandwich (link)