Summary

1/2/4-rail power bus with as many terminals as you want.

Instructions

Customize and select how many rails and slots you want, export an STL and print it. Once printed, you'll need:

one M4 rod per rail, 9 millimeters per slot on that rail
one M3 nut per slot
one M3x10 cap screw per slot

To assemble, just put the M4 rod in through the hole on the side, drop one M3 nut in each nut trap and screw in the screws from the sides. Insert cables from the top/bottom and tighten the screws, all done.

You can of course use longer screws, but they will stick out, which you probably don't want. (Especially if you're doing high voltage stuff...)

Customizable Power Bus