Well, things with iron. Apparently you can stroke a screwdriver with a magnet in the same direction over and over, like petting a cat, and turn it into one that hold onto your screws while you work.

It's always a mild force with those methods. A neodymium is inert until hit with a large electric charge. Larger the charge more magnetic force. No doubt there's an upper limit. Just bought a set of 100lbs/32kg pull for modding a video camera.