My neighbor found this metal tool in a box from his father’s workshop.
It's a cube with all sorts and sizes of circles and half spheres on every edge.
What is it?
Die for creating sheetmetal hemispheres. There should be a set of punches with round ball ends somewhere in that mix, unless someone misused them for something else or lost them.
Doming Block and Punch Set is one term for the tool set. The die is also called a dapping block. You can find them at jewelry tool suppliers.