Prototyping perfboard cut to Eurorack panel widths, so a circuit you are testing can live in the rack instead of on the bench next to it.
Twenty boards to a pack, five each at 6HP, 8HP, 12HP and 16HP. Two rows of pads, trace-connected to the adjacent through-holes, which covers most of what a utility module or a one-off CV tool needs.
I still cannot quite believe these did not already exist. Somebody has obviously had the idea, because it is close to the least clever one available in a hobby built almost entirely around small boards in standard widths. I looked anyway, could not find it anywhere, and made it instead.
They are for sale on Etsy for $35 a pack.