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Dasher is a computer accessibility tool which enables users to write without using a keyboard, by entering text on a screen using a pointing device such as a mouse, a touchpad, a touch screen, a roller ball, a joystick, a Wii Remote, or even mouses operated by the foot or head. Such instruments could serve as prosthetic devices for disabled people who cannot use standard keyboards, or where the use of one is impractical.
Whatever the writer uses as a pointer, he /she selects a letter from ones displayed on a screen, whereupon the system uses a probabilistic predictive model to anticipate the likely character combinations for the next piece of text, and accord these higher priority by displaying them more prominently than highly unlikely letter combinations. This saves the user effort and time as they proceed to choose the next letter from those offered. The process of composing text in this way has been likened to an arcade game, as users zoom through characters that fly across the screen in order to input text. The system learns from experience which letter combinations are the most popular, and changes its display protocol over time to reflect this.
Dasher is licensed under the GPL. It is available for several platforms including Mac OS, Microsoft Windows, Pocket PC, and Unix-like operating systems with GTK support.
Dasher was invented by David J. C. MacKay and developed by David Ward and other members of MacKay's Cambridge research group. The Dasher project is supported by the Gatsby Charitable Foundation.