Flutter is an interesting application for the Mac that lets you use hand gestures to control playback of audio from your Mac. If you think of Flutter as Kinect for the Mac, you'll get a good idea of what it does, although the current version is limited to audio file playback. Flutter is a free download and installs quickly and easily.
Once installed, you can use Flutter through the Mac's camera to control your audio file playback. You can hold up a palm to stop playback of an audio file, and you can stick your thumb to the left or right to move to next or previous song (or simply move through the current song). To use Flutter properly, you need to be in visual range of the Mac camera, a distance of up to about 6 feet. We tried Flutter with iTunes, Spotify, and QuickTime and it worked with all three, and we suspect it will work with other apps too.
The developers will be extending Flutter to work with other apps than music playback, but at the moment this is all it does. Having said that, it's really cool to load up and demonstrate to your friends. Since Flutter is free, if you play a lot of audio files on your Mac you should give this a try just for fun.