Indie makers RLT Industries of New Braunfels, Texas, sells this lovely wooden model kit of the classic “south-pointing chariot” mechanism. Set the chariot down with the vane pointing in an arbitrary direction — south, north, whatever — and a geared differential connected to the wheels will keep it pointing the same direction regardless of which way the chariot turns. Their version went through eight prototypes to get the gearing just right and seems like a helladeal at $59.