piano scale
A♭ major
A♭1B♭2C3D♭4E♭5F6G7
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 G♯ 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
A♭WB♭WCHD♭WE♭WFWGHA♭
What is true of it
A♭ major is A♭, B♭, C, D♭, E♭, F and G, and back to A♭.
Its steps are W – W – H – W – W – W – H, where W is a whole step and H a half.
On the same tonic, A♭ melodic minor differs from it by exactly one note.
Chords made only of these notes
Found by testing every chord in the catalogue against these 7 sounds, not chosen.