Miki wrote:

Maybe this is too far off-topic... but one day I was thinking how nice
it would be to put hydraulic motors onto two wheels of a trailer with
an appropriate power unit. That way you could maneuver the trailer
around without the tow vehicle, to park it in a tight spot maybe.
With two motors and the little wheelie thing on the A-frame you could
skid-steer it.

Powered hand truck type dollies for moving trailers exist, but they are
separate units that hook to the trailer using the normal hitch.

The only reason to go to the cost and effort of powering the trailer
wheels itself would be for something like off road use providing all
wheel drive.