Think of an A/B box. Do those exist in reverse? Say I have an expensive looper and don't want another, or maybe I have a talk-box that I want controlled by both a keyboard and a guitar without having to also switch what my mic is plugged into. Does there exist a pedal or something that has two inputs and one output, where the two inputs don't affect each other? I would be satisfied by something that doesn't even mix the levels of the two instruments, but other people may want that, so include that if there is one.