ARToolKit is a software library that can be used to calculate camera position and orientation relative to physical markers in real time. This enables the easy development of a wide range of Augmented Reality applications

Get it here ARToolKitPlus 2.0: http://studierstube.icg.tu-graz.ac.at/handheld_ar/artoolkitplus.php

Handheld AR project: http://studierstube.icg.tu-graz.ac.at/handheld_ar

Possibly homebrew Augmented Reality applications on the way by those who have the time to play with this