Harps are musical instruments that if you happen to hear a pro playing, you will be carried away. Marcan decided to make his own harp... but a string-less one. So, he used his laser projector that runs an OpenLase application which projects dots on the wall, like the keys of a piano. An old EyeToy that he had is used to "see" these dots on the wall from a very specific angle. OpenCV and some Python scripting is used to recognize the position of each dot, and if a dot is moved, the appropriate note is played from the speaker (with PyALSA). The following video shows how he made this harp, and also his musical skills (playing a very known tune). Visit his page for more.
And here is the same project but with vertical string alignment: