Bb Augmented Major 7th, 2nd inversion (F# in the bass)
Also written as Bbaug(maj7)/F#.
Notes, from the bass up
F# (bass)AA#D
The same notes as Bb Augmented Major 7th (F#, A, A# and D), rearranged so F# is the lowest note. Use it to move between chords with smaller jumps across the keyboard.