V-grooves that go most of the way through a PCB are one way to go about this, but a line of perforations along which to snap a tab is another. But what’s the best size and spacing of holes to use?

The project by [Jan Mrázek] is called KiKit and works on .kicad_pcb files to ... let you set space between the boards, number of boards in the grid, width of the tabs, tab dimensions, number ...