Renz Mute type II. Pretty rare these days, I imagine. Pre-dates the pedal tuner.
It's a passive, mute switch with tuner output. LED is green when output is hot, and red when muted (tuner out is always 'on').
Runs off standard BOSS-type adapter or 9volt battery (neither included).
Works great, sounds totally clean! It's cosmetically beat up & screws heads are a little bit stripped, but still functional. I toured and recorded with this pedal for years in over 30 countries across the globe, so there is some wear & tear! Still functions perfectly, however.
I think it cost close to $100 back in the day. I don't they are made anymore. $35 shipped to ConUS!