A few days ago I have created a plugin that tries to implement a simple guitar fretboard tool for tablature input and visualization, similarly to the existing Piano keyboard tool or similar fretboard tools in other score editors. The result looks approximately like this (see the full screenshot here):
This plugin currently supports both visualizing the currently selected chord on the fretboard and doing note input by adding new chords (in Note Input mode) or editing existing chords in the tablature.
The project has largely been started to explore possibilities the of plugins framework in its current (as per 3.3 RC version) state and to figure out whether this framework is suitable to extend MuseScore user interface in some reasonable way. The answer seems to be mostly "yes", although the plugins framework lacks an access to some aspects of information about a score (like staff/instrument properties) and means to trigger most of GUI events (like viewport positioning and doing chords playback without entering Play mode).
So I hope this project will be useful both for users working on tablature scores and for other plugin developers trying to create something similar. Any feedback, both on this plugin and on similar GUI plugins development in general, would be greatly appreciated!