piano scale
G♭ major
G♭1A♭2B♭3C♭4D♭5E♭6F7
The seven-note scale everything else is measured against: two whole steps, a half, three whole steps, a half.
The same sounds spelled from the other side are F♯ major.
Written out
Every accidental is written in, rather than left to a key signature, so the letters can be read one at a time.
The step pattern
G♭WA♭WB♭HC♭WD♭WE♭WFHG♭
What is true of it
G♭ major is G♭, A♭, B♭, C♭, D♭, E♭ and F, and back to G♭.
Its steps are W – W – H – W – W – W – H, where W is a whole step and H a half.
It costs 6 alterations to write — near the limit of what a key signature can carry.
On the same tonic, G♭ melodic minor differs from it by exactly one note.
Chords made only of these notes
D♭majorD♭7dominant seventhE♭mminorE♭m7minor seventhFdimdiminishedFm7♭5half-diminished seventhG♭majorG♭maj7major seventh
Found by testing every chord in the catalogue against these 7 sounds, not chosen.