In my 4th term at FH Hagenberg in Austria the "paintstation" was created. In a team of 7 we developed this virtual graffiti station, which allowes the user to spray virtually on every wall on this earth.
We used technologies like the openCV for tracking a infra-red point, wxWidgets for the GUI and openGL for painting.
During internship in 2006 at the research departement of the course information-design at fh-joanneum I developed the GMouse - which should be a mouse substitute. You can move the mouse by pointing with your hand, and click by bending a finger. Therefore I used a magnetic Polhemus Tracker to the 3D position of the hand and a data glove to recognize if a finger is bended.