The tractor beam, as it appears in science fiction, is usually applied to trapping or towing one spaceship from another (at least that's what they always seemed to do in the Star Trek TV shows).
However, if we had real tractor beams what might we use them for - since we don't have a lot of space-going starships to muck about with yet?
Well, thinking of a drastic change of scale, how about something that could grab and move (for example) kidney stones inside the body without any breaking of the skin?
Researchers in the UK have a working sonic device that can levitate small styrofoam balls, and one of the applications they can forsee would be something like the above.
[One of the researchers] explains that possible applications include trapping and moving kidney stones with medical imaging machines. Previously this wasn't possible due to the very small wavelengths they use to capture high resolution images. “Now, because we can trap particles larger than half a wavelength, you could use the same machine that is used for imaging for trapping particles,”PhysicsWorld