UDPATE: D'oh! It's a proof of concept rendering, not an actual coded App! My bad. (Thanks to Kevind for pointing that out in the comments)

What is iHologram? A simple application that fools your eye into seeing a 3D walking cartoon cat.

What does it do? Nothing but bring a smile to your face and a little magic to your iPhone.

Says Gizmodo:

David [OReilly]'s application assumes a constant viewing angle of 35 to 45 degrees, which is the usual when anyone watches the iPhone screen. Knowing that angle, the application calculates the orientation of the screen relative to the viewer using the iPhone motion sensors, so when you turn it around, the 3D world perspective gets skewed accordingly.