It’s a shoe called “Mobius”:
United Nude (!) issues this not-really-a-wedge in several heights and colors, at prices generally $100-200. Women I know with a grounding in mathematics will spurn this shoe because (1) it’s pricey for something so minimal and (2) it’s not really a Möbius strip, now is it? Well, no, it’s not. However, this is.
(Via ShoeBlog, which features several current designs by United Nude.)