There are numerous Modal tunings of which Modal D (DADGAD) maybe the most popular, its chords can have a deep 'ringy' sound. Modal tunings are most associated with Celtic music, they are also used in traditional English and Irish folk styles, Mountain Indian and Grunge.

"Modal" tunings are non-chordal tunings, Modal D (DADGAD) is an open D suspended fourth chord. Being suspended, the open tuning is neither intrinsically major nor minor which is why it is a modal tuning.