The TRX reverse fly works your rear deltoids and rhomboids.

TRX Reverse Fly Form Cue

Face the base point, hold onto the straps and walk your feet in front of you, leaning back, until your torso is at a 45 degree angle. Start with your arms straight out in front of you, then squeeze your back as you open your arms wide, keeping a slight bend at the elbows. Return slowly to start. Make sure to keep your torso in one straight line, like a tilted plank.