The Wheelee Board (1977) unquestionably was the oddest skateboard. Ever.
With six wheels and a plastic board with the rear wheels set at an angle, it was designed for tricks. I haven't had much personal experience with skateboards of any kind, but I imagine one would have to be particularly deft in their skills to ride these things. Or suicidally insane.
Not much else is known about the Wheelee Board, except that it's apparently a joke in the skateboarder community.