MEX is a gate row expander for the already extremely versatile Muxlicer sequencer.
MEX extends Muxlicer with a trigger output and activation switches per step. The three position switch is used to select one gate per step, no gate or as many gates as are coming from Muxlicer. What's really cool about MEX is that you can daisy-chain it with other MEXes and thus attach as many trigger tracks to a Muxlicer as you want.