piano scale
A♭ Mixolydian
A♭1B♭2C3D♭4E♭5F6G♭♭7
Major with a flattened seventh: the scale that fits a dominant seventh chord without altering it.
The same sounds spelled from the other side are G♯ Mixolydian.
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♭WFHG♭WA♭
What is true of it
A♭ Mixolydian is A♭, B♭, C, D♭, E♭, F and G♭, and back to A♭.
Its steps are W – W – H – W – W – H – W, where W is a whole step and H a half.
On the same tonic, A♭ major differs from it by exactly one note.
Chords made only of these notes
CdimdiminishedCm7♭5half-diminished seventhD♭majorD♭maj7major seventhE♭mminorE♭m7minor seventhFmminorFm7minor seventh
Found by testing every chord in the catalogue against these 7 sounds, not chosen.