Number 27: Big DogThe star of what may be MITs most popular YouTube video is a four-legged, gas-guzzling robot intended to serve as a pack animal for the military. More than 11 million people have watched BigDog climb a wooded hill, shuffle through deep snow, slip on ice, and deftly recover when knocked over. (It uses global positioning system coordinates to navigate.) Designed by Marc Raibert, who in 1980 founded MITs Leg Lab to help robots mimic human walking, and his team at Boston Dynamics, BigDog holds the record for distance traveled by a legged vehicle: nearly 13 miles. The project is funded by the Department of Defense, which recently gave Raiberts company a grant to develop Cheetah, a robot that could run faster than 20 miles per hour.