How about a 1-wheel tractor? The smallest tractor tested at the Nebraska Tractor Test facility was the "Choremaster B Gasoline". Back in 1950, the tiny tractor developed 1.47 & 0,77
HP @ 3600
RPM (belt & drawbar
HP). It sported a 5.89 cubic inch one cylinder Clinton air-colled engine, had one forward gear and would travel between 1-3/4 to 2-2/3 MPH. It weighed in at a mere 123 pounds................chim
Here's a pic of a Choremaster, although I'm not sure it's a B. There were other models.
http://www.ytmag.com/cgi-bin/gallery.cgi?ag17_060.jpg