I recently wrote this classical etude that was literally inspired by a type of slack key tuning - I like to call this tuning a 'C-minor open tuning':
string 6 - down by a major third to 'C'
string 5 - unchanged at 'A'
string 4 - unchanged at 'D'
string 3 - unchanged at 'G'
string 2 - unchanged at 'B'
string 1 - down by a half step to 'Eb'
This tuning forced me to play the guitar differently and I composed this piece, RED RUSHES BY, going mostly by ear and not using my brain so much. In other words, I literally wasn't trying to make sense of everything like I usually would and wasn't immediately able to use familiar shapes. It was a real pleasure to encounter all these different colors and, with two strings tuned down by quite a bit, the lower string tension caused the top of the guitar to resonate in a different sweet spot.
The right hand part utilizes only two fingers and the thumb and is quite quick to learn and get up to speed. Enjoy!