Drop D (DADGBE

The most frequently used alternate tuning and one of the easiest ones to work with. The only difference from standard tuning is that the low E string is tuned down to D. Examples include the Beatles’ “Dear Prudence,” Led Zeppelin’s “Moby Dick,” Nirvana’s “All Apologies” the Foo Fighters’ “Everlong” and Soundgarden’s “Black Hole Sun.”
Open D (DADF#AD

As the name suggests, basically an open D major chord. Used on the Black Crowes’ “She Talks to Angels” and much of Dylan’s Blood on the Tracks.
Open G (DGDGBD

They should just re-name this the Keith Richards tuning—heard on the Stones’ “Honky Tonk Woman,” “Brown Sugar,” “Can’t You Hear Me Knockin’,” “All Down the Line,” “Tumbling Dice” and “Start Me Up,” among others. Zeppelin made good use of it, too—“In My Time of Dying,” “That’s the Way,” “Dancing Days,” “Bron-y-aur Stomp” and “Black Country Woman” all being fine examples.
D Modal (DADGAD

An especially lush-sounding tuning. It is the secret behind the sweeping epic majesty of Zeppelin’s “Kashmir,” as well as “Black Mountain Side.”
Baritone (ADGCEA; perfect fifth below standard) or (BEADF♯B; perfect fourth below standard

A staple of 1960s country music. In rock music, the guttural almost-a-bass-guitar sound of baritone has been used by everyone from the Beach Boys (“Dance, Dance, Dance”) to Cream (most of Fresh Cream) to the Cure (“Carnage Visors,” “Pictures of You”).
AND LETS NOT FORGET THE GODFATHER OF HEAVY METAL DROP TUNING TONNI IOMMI