This a drive, based on 4 omni-wheels, wheels that have 2 Degrees Of Freedom, allowing them to move in more directions than forward and back.

This allows for design of a based that can move in the X and Y directions without needing to turn, and also rotate while maintaining a straight line - giving the mobile base a full 3 degrees of freedom.

Charmed Labs produce a set of these that can be used with standard Lego axles.

I am still researching into who actually developed them - I know there has been more than one attempt to patent them.

(paid links)