Open E tuning
The open E tuning is a rather popular alternative for guitar slide players, but can work as a way to find new song ideas regardless of the style.
You should be aware of that this tuning put some extra pressure on the guitar. This is because three of the strings are tuned in a way that increase the tension on the neck. A "safe-mode" is instead to tune to the Open D with a capo on 2nd fret, which will be the same as Open E.
To get the open E tuning on your guitar you tune it like this: E B E G# B E.
Including an octave perspective, the tuning is written E2-B2-E3-G#3-B3-E, meaning that the lowest string is an E note on the second octave, the second lowest string is a B note on the second octave and so on. Standard tuning reference: E2-A2-D3-G3-B3-E4.
Movable one finger (or slide) shapes
All you have to do is to lay your fingers over the four highest strings. or play on all six strings. As the pictures illustrate, the E 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 E:
E: 000000 / 000004
F#: XX222 / 222222
G: XX3333 / 333333
A: XX5555 / 555555
B: XX7777 / 777777
C#: XX9999 / 999999
D: X X 10 10 10 10 / 10 10 10 10 10 10
Some other movable chords:
Joni Mitchell used this tuning for her famous song "Big Yellow Taxi" including the chords A (555555), A6 (575555), B (77777), B6 (797777), E (000000), Aadd9/E (020100).
E7 could also be played as XX0654 or XXX654, which formally will result in E7(no5). A7 is to be correct A7/E. If you prefer, A7 could also be played as XXX123, which formally will result in A7(no5). If you prefer, B7 could also be played as XXX345, which formally will result in B7(no5).
A way to decrease the chord movement between E7 and A7 is to instead play A7 as xx3555.
These are some of the chords you could play in first-position when using the E open tuning. When playing in the key of E major, there are few good alternatives for the V chord, mainly because of the position of the D# notes.
There are many alternatives for some of the E chords. For example, E6 could also be played as 000024.
If you want to go more into depth of this particular guitar tuning, see the Essential Chords in Open E Tuning ebook with over 100 chord diagrams.