Guido Vigevano designed it in 1335, describing it as a "waggon which is propelled by the wind without draught animals, and which dashes violently over open country to the confusion of all troops"
No Tech Magazine writes:
Guido Vigevano's wind-propelled battle wagon was designed as a weapon in the crusades. But the wind conditions and the scarcity of flat and smooth terrain made it so that the car was never built (although the inventor probably constructed a scale model). It is remarkable that Vigevano imagined a wind car powered by a vertical windmill [sic-see Jeremiah's comment] (hot and sophisticated technology in those days), rather than using a low-tech sail (which the Chinese had done centuries before).
Guido von Vigevano : "And thus waggons are finished which are propelled without draught-animals and without wind, of which every part can be carried in pieces on horseback and the assembled in a single day or night, from which may ensue much of benefit to the recovery of the Holy Land."
A sample of the original drawings. More at No-Tech Magazine