A Fretter Box
I am not sure of something like this exists already but here is a simple tool I thought up and built for making my new fret boards. It can layout custom fretboard lengths or double-check existing fret boards before attaching to the dulcimer. Simply place the fretboard blank on the box, with the bridge and nut either inset or clearly marked. Tighten the tuning string to the key you want. Then use the noter to locate the exact place for each note (I use an electronic Snark) and mark them on the fretboard. It has two string options for Just Scale fretting as well. Carefully scribe using the T-Square across the board. Cut the slots and install the frets.