They’re pizza cutters. Not sure if you’ve seen them before, but they’re metal disks with a sharp(ish) edge that spin freely. You use it by pressing it into the pizza then pushing forward so the disk rotates and cuts through the pizza. Not as easy or precise as using, say, a mezzaluna, but much more compact and easy to fit in a drawer. This is what a more typical design looks like:

Picture of a pizza cutter