The Four Banger is a booster pedal for electric guitar. The pedal contains four different booster circuits that each have their own separate boost volume knobs and their own on/off switch; this enables more than one boost to be used simultaneously. The different boosters are as follows: a Germanium Treble boost in the style of the classic Rangemaster, a super-clean Opamp boost (original design), a MOSFET boost (in the style of a certain popular boost with gain control that crackles), and a JFET mu-amp boost based on the popular DIY MiniBooster designed by Jack Orman. They are stacked in series, which enables different combinations of overdrive and fuzz.
I absolutely ripped @$$ last night at that gig, especially when I plugged in my trusty old four banger.