This is tuning is probably the simplest conversion of the standard Guitar tuning to open tuning.
We simply turn the A2 string to an B2 string, Because of the D3-G3-B3-E4 part it has two rows of easy minor-major triads with 2 or 3 only frets. An advantage is that it contains at an interval of 5 which sounds good in an open chord. It is the 5-3m-4-3M-4 tuning
The next tool can calculate the chords
https://www.gtdb.org/ebdgbe
As an alternative, we may apply the 5-5-4-3M-4 E.g. C2-G2-D3-G3-B3-E4, for both the Oud and the 6-string guitar.
The D3-G3-B3-E4 part is a 4-string Greek Bouzouki in G major
The G2-D3-G3 part is a 3-string Greek Bouzouki in Bb major
The C2-G2-D3-G3 is a bass Irish 4-string Bouzouki
The C2-G2-D3 is a low tambouras or saz.
We can have this tuning also in reflected form in other words
4-3M-4-5-5 E.g. C2-F2-A2-D3-A3-E4 .
The 4-3M-4-4-4 or C2-F2-A2-D3-G3-C4 is one of the standard tuning of the OUD.
But we can have also its reflected version like
4-4-4-3M-4 E.g. E2-A2-D3-G3-B3-E4 which is of course none other than the stanrd of the guitar.
