It's a thingy that vibrates the strings to break in a guitar. IMO, it is a poor substitute for patience and practice. I hope I never decide to use one, as I believe it could, actually, be detrimental to the guitar over it's lifetime. There is no substitute for playing a guitar, and breaking it in to the player. It may boost the sound a bit, initially, but then the player has to re-break in the guitar anyway, as it will not be the same type of vibration that the ToneRite provides. It's like giving your guitar to someone else, who plays poorly, and only on a few frets, to break it in for you.
Check around the internet, there are plans for making them with aquarium pumps, if that tells you anything about the type of vibration that is involved!