Reality Slice is an augmented reality application that lets you use your iPhones camera to slice food such as pizzas and cakes into evenly-sized portions easily.
Simply choose the shape of the food, and the number of slices required, and press the Go button. You will then be presented with a camera view, overlaid with grid lines showing exactly where you you need to cut.
The lines are adjusted in 3D using your iPhones motion sensor to ensure they are still accurate, even when you hold the phone at an angle.