This is a handy little device - it's good for one thing only, that is cutting plasterboard, but it's very good at it.
It has two main body parts as you can see, with a gap between them. The body parts are attracted together by powerful magnets but a gap is maintained between them by hinged spacers, and there is a cutting blade prodtruding on each side of the gap.
You push plasterboard into the space between the bodies, or rather you slide the cutter's handle part along the top of the plasterboard and the bottom cutter part follows along underneath. The spacers hinge out of the way, and the magnets hold the two bodies tight against the plasterboard so the blades then cut both sides of it. You can then snap the board. The blades are elongated so it tends to cut in straight lines, although it will do curves.
They call it a blade runner, and I couldn't find a supplier in Europe. The best I could find was one in Australia, and it cost me more to ship it than to buy. There's an opportunity here for an enterprising importer.