I recently got to try out a more violent and thus fun to play with mechanical vibration machine that is aimed at treating tense muscles. The device not just produces a minor buzz but really goes at it. The amount of action is so much that (in all likelihood) it probably should not be sold in places where litigation is encouraged by court systems. But, see for yourself.
This thing called "Sissel PRO Intensive Massager" [link] has two nubs that will, alternatively, press down into your skin.
Links to buy the device:
This is a video showing how the device works, recorded at normal speed. As one can see the vibration occurs rather fast.
Watching fast action for massaging muscles and tendons is not as much fun as seeing the amount of massaging being done with more detail. So here we are, as slow motion video. As we see, the arm gets a pretty comprehensive treatment.
A very slow motion video.