OK, this isn't designed for a motorcycle but the possibilities are obvious. The Ktrak rear drive kit and optional ski kit transform your mountain bike into a snow bike. If your bike has quick release hubs, no tools are needed, you just swap out the wheels with the rear track and front ski and off you go. Considering all of the attention the Hyanide and Baal tracked motorcycles generated, something like this gets the wheels turning.
Sure, you can get a snowmobile for the winter months but even living in the snowy north as I do, sleds can be a real money pit if the snow is light. Suppose you could swap out the rear tire of your motorcycle with something like this. Obviously, not all motorcycles would be good candidates for a rear track and front ski but some bikes, maybe a dirt bike, might be fun if you could do this.
The Ktrak comes in versions for both adult and children's bicycles. The adult version is $400 for the rear drive kit and $140 for the ski. Children's versions are $200 and $90 respectively. It will be available in January.
UPDATE: That was fast! Thanks to a comment by Mark, it looks like this is already available for motorcycles. SwitchTraxx Thanks, Mark!
UPDATE 2: Thanks to P.T. Anderson, now we also know about the Snow Hawk. Not a conversion but same rear track and front ski setup in a single line with a motorcycle riding position.