[CRConrad]

The geometry, with the front and rear axles turning on opposedly-angled tilted axes, looks identical to that of (the old four-wheeled kind of) roller skates. Swiveling the axles into a turn makes the whole thing tilt -- and conversely, tilting it swivels the axles so it turns.

[CRConrad]

And of course, come to think of it, skateboards.

Were those originally invented by nailing rollerskate trucks under a plank, or what? I'm fairly sure skateboards use bigger -- certainly wider -- trucks nowadays, but rollerskates definitely predate at lest the "modern" (i.e. post-1970s) skateboard boom... Just a WAG.