Interesting. I’ve just had a look at what FolkTab do. They are using lilypond (converting files from abc as needed) to produce the tab.

Some details here

The version of lilypond on the Linux distro for my PC has:

guitar-tuning (e, a, d g b e')
guitar-seven-string-tuning (b,, e, a, d g b e')
guitar-drop-d-tuning (d, a, d g b e')
guitar-drop-c-tuning (c, g, c f a d')
guitar-open-g-tuning (d, g, d g b d')
guitar-open-d-tuning (d, a, d fis a d')
guitar-dadgad-tuning (d, a, d g a d')
guitar-lute-tuning (e, a, d fis b e')
guitar-asus4-tuning (e, a, d e a e')

%% bass tunings
bass-tuning (e,, a,, d, g,)
bass-four-string-tuning (e,, a,, d, g,)
bass-drop-d-tuning (d,, a,, d, g,)
bass-five-string-tuning (b,,, e,, a,, d, g,)
bass-six-string-tuning (b,,, e,, a,, d, g, c)

%% mandolin tunings
mandolin-tuning (g d' a' e')

%% tunings for 5-string banjo
banjo-open-g-tuning (g' d g b d')
banjo-c-tuning (g' c g b d')
banjo-modal-tuning (g' d g c' d')
banjo-open-d-tuning (a' d fis a d')
banjo-open-dm-tuning (a' d f a d')
banjo-double-c-tuning (g' c g c' d')
banjo-double-d-tuning (a' d g d' e')

%% ukulele tunings
ukulele-tuning (g' c' e' a')
ukulele-d-tuning (a' d' fis' b')
tenor-ukulele-tuning (g c' e' a')
baritone-ukulele-tuning (d g b e')

%% orchestral strings
violin-tuning (g d' a' e')
viola-tuning (c g d' a')
cello-tuning (c, g, d a)
double-bass-tuning (e,, a,, d, g,)