It's a die cutting machine for fabric. There are lots of Youtube video demonstrations of it; just search on Accuquilt Go. (Be aware that most of the demo's show lots of fabric waste; there is actually very little waste if you position fabric at home -- very similar to the waste from cutting with a ruler.)
I find the Go! most useful for cutting triangles -- very exact cutting with the dog ears lobbed off. The triangles are cut so perfectly it's really easy to match them for sewing. It is also great for odd shapes, rag squares, and fusible applique. If you have difficulty cutting straight strips without "bends" in the middle, then it is great for that too. (I personally prefer the June Taylor shape cut mat for cutting strips.)
Manufacturer's website is
http://www.accuquilt.com/ but I think the Youtube videos are more helpful.