Hi, Dave. I have owned a WoodRat since 2006. In operation it behaves much like a Vertical Milling Machine. It uses your router, and can move and control the bit in any of the 3-axis. X-Y-Z. And it provides clamping a board in about 3 orientations.
The manufacturer claims it does away with the need of a router table. Not entirely a true statement. If you are doing edge profiles on large, long or heavy sheets or timbers, a router table would be easier and safer.
Where the WR shines is in making joints. It will make beautiful Dovetails, Finger (comb) Joints, Mortise and Tenons. The tooling can equal the cost of the machine, but you don't need jigs. In some cases you might want a jig, and some of these can be made in the shop.
One most people might want helps in clamping long pieces for cutting a mortise. You can make one yourself in about an hour. Two others that are sold by the company and by the Craftsman Gallery in Ohio are useful for cutting compound angled tenons for chairs and for doing flat work need in making boxes. Or inlay.
Unless you were a machinist, it would be cheaper to simply buy the machine. They turn up for sale from time to time on eBay and the WoodRat Forum. Send me an email and I'll send you back a free 43-page instruction guide for the machine. [email protected]