This device was invented at Taylor guitars by the great tooling-whiz minds there many years ago. When I spent a couple days there learning the way they do things 15 years or so ago, I saw this tool in use at the factory, and had to have one. They are since available through Stewart-MacDonald supply, and are worth every penny.
When refretting an acoustic guitar, there has always been the issue of laying the frets in the fretboard extension over the body. One can't simply pound away in this region, as the top will vibrate, and it will be very hard to get the frets in due to the movement of the wood. It is also common for people to loosen braces and damage the top this way. It is common for repairmen to hold or rig a bag of buckshot under the top from the inside to absorb this shock. Another way that I don't like, is to simply route out the slots and drop the frets in with glue to avoid the issue all together.
The Taylor Fret-Buck solves this completely. It slips in through the hole, rests atop the guitar with thick cork pads, and a cork-lined pad on a swinging jaw comes up from below to tighten to the cross brace. All vibration is dampened, and one can tap in the frets nice and clean with no risk or movement to the top! It actually makes the fretting process go easier on the rest of the neck too, as it dampens the vibration along the entire length. This also help vintage guitars as the lack of vibration is healthier for old binding, delicate finishes, and brittle hide glue that could be compromised.