Known as M-Blocks, the robots are cubes with no external moving parts. Nonetheless, they're able to climb over and around one another, leap through the air, roll across the ground, and even move while suspended upside down from metallic surfaces.
Inside each M-Block is a flywheel that can reach speeds of 20,000 revolutions per minute; when the flywheel is braked, it imparts its angular momentum to the cube. On each edge of an M-Block, and on every face, are cleverly arranged permanent magnets that allow any two cubes to attach to each other.
Read more: http://web.mit.edu/newsoffice/2013/simple-scheme-for-self-assembling-robots-1004.html
Video: Melanie Gonick, MIT News