$33A/B is a dual switch with convenient normalizations. Since the module is passive, the common jacks can be used either for routing an input to alternate outputs, or routing two alternate inputs to an output. Using both switches together, A/B routes an input to an output across two effects loops. Without anything plugged in, the jacks are normalled together, giving you a bypass switch.
A/B is only available as a DIY kit. With only 7 parts and no power, A/B makes an excellent introduction to DIY. No power means no “magic smoke” when you make a mistake. Comes with everything you need. Just add solder.