It does what its' name implies, it cuts strips and circles for you. Both Glastar and Inland make comparable models, but inland has come out with a new model that allows you to use your own cutter, hopefully a Toyo supercutter, and not the typical plain steel six-wheeled cutter. You can also lock in a pen or pencil for drawing, or an x-acto blade for cutting paper or sandblasting resist.
The Glastar and Inland models can cut a 5" to a 24" circle. There now is a new model from DiamondTech that can cut smaller circles, from 1/2" to 5".