With Suspended Motor Action!
This is a gloriously disturbing device I found lurking under a sink in my parents' house, and they let me keep it. Manufactured in the 1950s by a company that also made hair clippers and food processors, it consists of an electric motor suspended between two bearings over an aluminum base. Affixed to the bottom of the base is a sponge rubber cushion, as well as two sets of three coiled metal straps. Designed for use with standard 110 volt wall current.
The device is strapped to the back of the hand -- slide four fingers through the rearmost set of straps, with only your ring finger and middle finger going through the front set. There. Now you look like you belong in a Nine Inch Nails video.
When switched on, the Massage Modality makes your hand vibrate. Intensely. "This construction delivers several thousand controllable rotating-patting massage movements to your fingers per minute." Then you grasp and stroke whatever flesh you want massaged. I can't make any statements on how useful it is as a relaxation aid, because everyone I've threatened to use it on tensed up as soon as they saw it. It certainly makes your hand numb, though. I will leave the possibility of other uses for it as an exercise for the reader. Suffice to say that Oster produced a related model call the Stim-U-Lax Junior.
Note: I'm pretty sure I saw Michael Palin's character use this or something similar in the movie Brazil.