GNU Backgammon is a world class backgammon application, and it works on many operating systems. It can play, analyse and teach backgammon. Its evaluation engine is based on artificial neural networks. It is currently a work-in-progress. So far it is able to play both independent games and tournament matches, evaluate and roll out positions, tune its own evaluation functions using either TD or supervised training, maintain databases of positions for training and other purposes, and more. See the following section for a more complete list.It is driven by a command-line interface, and displays an ASCII rendition of a board on text-only terminals, but also allows the user to play games and manipulate positions with a GTK+ board window (png 117k) where available. GNU Backgammon is extensible on platforms which support Guile and/or Python.