The Electro-Harmonix EchoFlanger is multi-effect producing flanger, chorus, delay, filter effects all in one pedal. The idea is not so common today but back in 1977 it was revolutionary for a guitarist. The Boss, Roland, Ibanez, Carl Martin, Zoom mulit-effects units didn't exist. Electro-Harmonix however is good like that. It's a very innovative company.
This is one hard pedal to find. I believe production totals were limited. The pedal is in very good condition and works great. It's got a sound that's often imitated but not quite duplicated. Kurt Cobain had one on his pedalboard rig.