A double A/B box for routing two guitars to either of two amps.
Say you're out on a gig playing both acoustic and electric guitar and you're using two amp but only one pedal board. The solution is very simple! Connect the two guitars to the instrument inputs and run the output to the pedal board. Then run the board out to the Route Box amp select input and the outputs to the two amps. This way you can route either of your two guitars through the pedal board to either of the two amps.