add mountain dulcimer incl. a tab preset
Currently, MuseScore does not allow to enter tabs for diatonic fretted instruments. This request comes up regularly.
It mainly concerns the mountain/appalachian dulcimer instrument (https://en.wikipedia.org/wiki/Appalachian_dulcimer), whose roots are European with the zitter family: https://en.wikipedia.org/wiki/Zither
It also concerns instruments of early music, the renaissance cittern, see here: https://en.wikipedia.org/wiki/Cittern (and here, end of page: http://www.cittern.theaterofmusic.com/faq/index.html)
But also contemporary derivative instruments eg among others: http://www.seagullguitars.com/en/products/m4 (discussion: https://musescore.org/fr/node/123921)