Old Blood Noise Endeavors AB/Y Switcher

They say:

Our AB/Y Switcher is a classic for a reason. Use two footswitches to independently connect A or B to Y, or both A and B to Y at the same time. This passive circuitry is commonly used to switch between instruments at the start of a signal chain, or outputs at the end.

AB/Y can pass signal without power, but the LED indication requires a 9V DC center negative 2.1mm jack power supply capable of 10mA (not included).

For more information, see the AB/Y manual, available here.