it started development as an orchard tractor by W. Chandler Knapp in New York and was briefly called the Knapp Farm Locomotive. In 1914 it was bought by the Gray Tractor Company and it was renamed the Gray Tractor, model A 20-35. A model B 15-25 was also added and later an 18-36 and 22-40 canadian special were added and the company folded int he early 30's.
From my understanding they are a real experiance to drive, and an absolute beast to steer with the large drum drive. I have read they were actually more popular in europe as "the American tractor" than here and a number survive over there. I have also heard that despite starting as an orchard tractor, they actully developed a set up to allow a plow, a disk and a planter to all be mounted to the sides and behind at the same time so three operations could be done each pass.