Open D tuning
The open D tuning is especially popular among guitar players who uses a slide, but it is also related to the folk genre. (Open D Tuning is not to be confused with Drop D tuning.)
When you retune your guitar, it is important that you turn the tuning pegs in a direction that decrease the string tension and not the opposite.
To get the open D tuning on your guitar you tune it like this: D A D F# A D.
Including an octave perspective, the tuning is written D2-A2-D3-F#3-A3-D4, meaning that the lowest string is a D note on the second octave, the second lowest string is a A note on the second octave and so on. Standard tuning reference: E2-A2-D3-G3-B3-E4.
Blues chords for 12 Bar
D7: you can also play on the 5th and the 6th string (000334). And you can play with the 1st and 3rd strings open as well (000030).
G7: an alternative is to include the 6th open string and in that case mute the 5th. The correct name of the chord is in both cases G7//D.
A7: this is to be correct an A7no3, meaning that the third note (C#) is missing.
These are some of the chords you can play in open position when using this particular tuning. You could in some cases skip the 6th string, for example, without playing on the six string the presented diagram with C/D would be C.
Because of the way the tones are configurated, there are few good alternatives for F# minor chords. A suggestion is to play F#m7 as 4420xx.
A regular E minor can't be to play in open position since neither E, G or B can be played on an open string. One way to play it in closed position is 2221xx.
Movable one-finger (or slide) shapes
All you have to do is to lay your fingers over the four highest strings. You can also play on all six strings. As the pictures illustrate, the D chord can be played with all open strings.
The shapes are movable, so if you move the fingers two steps up the fretboard from G major you will get an A major.
All common major chords in open D:
D: 000000 / 000004
E: XX22222 / 222222
F: XX3333 / 333333
G: XX55555 / 555555
A: XX7777 / 777777
B: XX9999 / 999999
C: X X 10 10 10 10 / 10 10 10 10 10 10
Movable slash chords, some examples:
Slash chords with A or D as bass note:
In the style of Keith Richard
Keith Richard uses open tunings including Open D. If you're interested in typical chords, here are some (all used in "Street Fighting Man"):
C: 10 10 10 10 10 10
Fadd9/C: 10 12 10 11 10 10
If you want to go more into depth of this particular guitar tuning, see the Essential Chords in Open D Tuning ebook with over 300 chord diagrams.