Quick Answer: A snowmobile, also known as a snowmachine, motor sled, ski-doo, motor sledge, skimobile, snow scooter, or simply a sled is a motorized vehicle designed for winter travel and recreation on snow. Their engines normally drive a continuous track at the rear, while skis at the front provide directional control. The earliest snowmobiles were powered by readily available industrial four-stroke, air-cooled engines. These would be replaced in part by lighter and more powerful two-stroke gasoline internal combustion engines. The challenges of cross-country transportation in the winter led to the invention of an all-terrain vehicle specifically designed for travel across deep snow where other vehicles foundered. As of 2003, the snowmobile market has been shared between the four large North American makers and some specialized makers like the Quebec-based AD Boivin, manufacturer of the Snow Hawk and the European Alpina snowmobile.