A tricked out Bombardier run by a tour company based in West Yellowstone.
Snowmobiling in Yellowstone is now only as part of guided tours with approved guides.  Too many snowmobiles chasing animals.
The same as #4 but the owner, a construction company renovating an isolated hotel during the winter, replaced the military cab with a Chevy pickup cab.  It has two trailers attached and the tracks on both are driven.  That must be a fun rig to backup.
Classic original Bombardier snow coach still used around the Snow Lodge at the southern end of the park.  It is noisy (you wear earplugs), uncomfortable, and faster than the 4 track modern units.  This one was at the Canyon Visitors Center
Designed for the Italian Army and used by the hotels to transfer luggage between the two hotels that are open in winter.  Both the tractor and trailer tracks are driven.   The tractor unit cannot steer by itself, the connection to the trailer is articulated so it can only steer if it has at least one trailer attached.
See photo in original gallery.