DADGAD
Celtic, UK folk-type and "moody" fingerstyle type and what I can only call quasi-classical guitar music for lack of any label I'm aware of.

Open G (D-G-D-G-B-D)
My most often used open tuning by a long shot... basic go-to tuning for all slide styles... covers most all genres
This is also known as Hawaiian slack key and is the most commonly used tuning for that genre

Open D (D-A-D-F#-A-D)
Very little slide, mostly fingerstyle Celtic, UK-folk style

Others, rarely used:

Drop D (D-A-D-G-B-E)
Just sets up a low D drone string. Use sometimes in Celtic and UK folk-type.

C6 (C-G-C-G-A-E)
slide only - use this to imitate a pedal steel (without pedals) or lap guitar
limited genre for me... western swing. I don't play country music, but one could use it for that genre too I suspect.


I play the open tunings only on acoustic guitar, with two exceptions... an electric in Open G for slide blues and an electric in C6 for western swing.