A Konoid is an artistic representation of a mathematical object called Sphericon.
It’s hard to believe that being placed on a slanted flat surface it rolls freely in a straight line.
Well it wobbles a little, but it will not stop.
It's available in three different sizes and many materials
From Wolfram MathWorld:
A sphericon is the solid formed from a bicone with opening angle of 90 degrees (and therefore with a=r=h) obtained by slicing the solid with a plane containing the rotational axes resulting in a square cross section, then rotating the two pieces by 90 degrees and reconnecting them.
A sphericon has a single continuous face and rolls by wobbling along that face, resulting in straight-line motion. In addition, one sphericon can roll around another.