YouTube member TheAussieInLA puts together his DIY version of the SpiderTrax rotational dolly and gets some pretty cool results. Looks like some basic skateboard trucks, skate wheels, and flat steel. [Thanks Alex]
The original version sold at PhotographyandCinema.com is no longer available, but if you're not the DIY type the next best version for the cheapest price is made through Konova. The Konova rotational dolly is well built with an anodized plating and a few fancy graphics. Although they opted to use roller blade type wheels, they flipped the axles upside down and shaved them flat, bringing it closer to the ground for low shots. You can find them following the link below.