Microsoft's Kinect paired with the Qt tool-kit can allow using your hand as an input device, or what the developers are calling an "air cursor" for this open-source project.
From the Maemo.org blog post, "As part of the SmarcoS project, we've been working on making the Kinect work as an input device for Qt applications. Basically you move your hand in the air, and are able to grab and drop things on the screen. We call this the Air Cursor."
The Qt Air Cursor is LGPL licensed and built atop the OpenNI library and OpenCV. Code for Qt Air Cursor can be found on GitHub.
Embedded below is a video of Qt Air Cursor in action.