A Natural User Interface is a user interface that allows humans to communicate with the computer using standard modes of human communication such as speech or gestures, and to manipulate virtual objects in a fashion similar to the way humans manipulate physical objects
The GML toolkit offers a number of modern services to developers of interactive applications. GML provides a number of ready-to-use input services with a friendly interface, based on computer vision techniques. This includes, but is not limited to: finger tracking for augmented surfaces, video capture and streaming, or user head tracking.
GML is a C++ library with a Tcl API, and uses an extended Tk canvas for user interface. Source code: [1 ]