Dasher is an alternate text input method, suitable for use with eye trackers, the mouse, or any other pointing device.
Rather than arranging the letters in the usual QWERTY style, Dasher puts the letters in alphabetical order at the right side of the screen, each letter within its own colored region. The size of the region--the amount of vertical space it occupies--is determined by a predictive algorithm, so that more likely next letters occupy more space and are, therefore, easier to aim for. Additionally, likely word completions 'bulge out' toward the left, so it is possible to simply aim for the whole desired word.
It is easier to understand by seeing it in action: