Open A tuning
Open A tuning is less common than Open G and it also puts more pressure on the strings and the neck. You can emulate Open A by putting a capo on the second fret when your guitar is tuned to Open G.
Otherwise, the tuning for Open A is: EAEAC#E.
The strings that differ from the standard should be turned so the string tension is decreased and not the opposite.
The Open A is quite popular in blues and was used a lot by John Lee Hooker. A collection of chords with diagrams will follow.
More info
Including an octave perspective, the tuning is written as E2-A2-E3-A3-C#4-E4, meaning the lowest string is an E note in the second octave, the second lowest string is an A note in the second octave and so on. Standard tuning reference: E2-A2-D3-G3-B3-E4. Open G tuning reference: D2-G2-D3-G3-B3-D4.
Major chords (movable shapes)
A
D
E
Comments
The shapes are movable and you have only to lay your fingers across the fretboard. As can be seen in the diagrams, the lowest string is not included but there is an option to do this as well. By playing 000000 instead for X00000 the chord spelling will be A/E.
List of major chords in open A:
A: X00000
B: X22222
C#: X44444
D: X55555
E: X77777
F#: X99999
G: X 10 10 10 10 10
See below for PDF chord chart ("Essential Chords in Open A Tuning ebook") for many more movable chord, voicings, progressions etc.
Minor chords (movable shapes)
Bm/F#
F#m/C#
Comments
Major chords can be extremely easy in this tuning, but minor chords are trickier. You might recognize the Am-shape here, but besides the fingers in the Am-shape you add two notes on the bass strings by placing your thumb over both the strings. You can leave out the 6th string to avoid playing the chords inverted.
You could instead use open position chords, which in most cases are more natural for the fingers:
Minor chords (open positions)
Em/G
F#m
Am
C#m
7th chords (movable shapes)
A7
B7
D7
E7
Blues shuffle
One way to play a blues shuffle is using these movable shapes (examples for D):
D5: X555XX
D6: X575XX
D7: X585XX
Progressions
One example of progression in this tuning:
A/E (040030) – Dadd9/E (050050) – Eadd11 (070070) – F#m7/E (090080)
This was an introduction to chords in open A tuning.
If you want more chords and progressions for this particular guitar tuning, see Essential Chords in Open A Tuning with over 300 chord diagrams (ebook with PDF chord charts).
Alternative Open A tunings
Besides the E-A-E-A-C#-E version presented here, Open A tuning can also be configured as E-A-C#-E-A-E. This version deviates from the common featured also seen in Open D, Open E and Open G with the possibility to play a 5th chord on the three lowest strings.
The Open Amaj7 tuning (E-A-E-G#-C#-E), is possible but not very popular. It has the advantage/disadvantage, depending of point of view, of including the A note only once; it also puts less pressure on the G-string.
See also open E tuning and drop C tuning