Double Drop D tuning
The Double Drop D tuning is the beautiful land of drone-like voicings.
Here is how you tune the guitar: DADGBD, which is almost similar to the Drop D tuning. The Double Drop D is suitable for a style somewhere between rock and singer-songwriting, for example, in the neighborhood of Neil Young, whereas Drop D is often used in rock context.
As you can notice, many chord diagrams are centered round the D tone and other chords in the key of D. But also playing in the key of G and Em would include most of the chords. The D minor key on the other hand do not partner well at all.
Concerning the G chord (5X005), notice that the three open strings actually create the G chord by their own, and therefore you could experiment by moving the lowest and highest notes. For example, 3X0003 would be a G/F and 7X0007 would be a G/A and 9X0009 would be a G/B. As a consequence, 0X0000 would result in G/D.
Apart from the presented diagram, there is unsurprisingly many more ways to play various D chords. One example is Dm that also could be played 003230.
A more problematic chord among those often used in D major key progressions is the F# minor. There is hardly any easy fingerings at all for this chord.
A chords in this tuning will, in general, produce a somewhat dissonant sound when the highest and/or lowest strings are included (because of the clash between C# and D notes). This is extra noticeable in chords such as Amaj7/D (002120).
Some suggestions of chord progressions in this tuning:
D - Dsus4 - D - Dsus4 - D
It will sound cool if you just strum the highest strings when playing Dsus4. Dsus2 could by the way be played as 000232 or, which may sound better, as 002232.
Amadd4 - Em
F#m/D - Em7
Bm/D - G - Em7
This tuning isn't particularly associated with blues, but here is a simple idea:
D7 (054530) - G7/D (0 10 9 10 8 0) - A7/D (0 12 11 12 10 0)
D7 (004530) - G9/D (0 0 9 10 8 0) - A7/D (0 0 11 12 10 0)
Here is some additional chords in the Double Drop D tuning listed in short notation:
Dm6: 003200 / 000203
If you want to go more into depth of this particular guitar tuning, see the Essential Chords in Double Drop D Tuning ebook with over 100 chord diagrams.
This was an introduction to the Double Drop D tuning on guitar, see also Drop C tuning.