Perhaps the single most numerous small business enterprise is container drayer. Individuals buy a tractor and then hire themselves out as independant contractors to container drayage companies. They haul the shipping containers back and forth from the port to virtually every point in the USA.
Sometimes they own more than one or two tractors and hire someone to drive the second. It is the most basic of businesses, one person, one piece of equipment very tightly focused on a market clamoring for folks to do the work.