The Army is experimenting with a four legged walking robot. Looks pretty much like a mechanical mule. Can pack 340 pounds and has a range of 12 miles, and a speed of 4 mph. It's autonomous, able to find it's own way, does not need a driver.
Looking at the picture, I keep wondering if it is any better than a real mule. It certainly won't be as quiet, what with an engine racketing away.