B Augmented Major 7th, 3rd inversion (A# in the bass)
Also written as Baug(maj7)/A#.
Notes, from the bass up
A# (bass)BD#G
The same notes as B Augmented Major 7th (A#, B, D# and G), rearranged so A# is the lowest note. Use it to move between chords with smaller jumps across the keyboard.