I saw this video this morning and thought: 'The guy who invented those wheels is a genius'. So I did a little looking.
It turns out that those wheels are called 'Mechanum' or 'Mecanum' wheels. A US patent was filed for in 1972 and obtained in 1975 by Bengt Ilon while he was employed by a Swedish company called Mecanum AB. The US Navy bought the patent and licensed it to various manufacturers in the 1980's.
The wheel works by providing a an axis of rotation 45° to the plane of the wheel. The vehicle moves sideways when the front and rear wheels move in opposite directions to each other. This works because all the wheel surfaces together form a complete 'unbroken wheel periphery' when moving laterally. In other words, rather than the wheel surface being confined to a single hub on an axle the wheel surface in the direction of travel is formed by all four of the wheels. Each wheel contributing a small piece of the complete circle.