This is the Prophet-600 Panorama Mod board integrated in Sequential Circuit's famous Prophet-600 analogue synthesizer from the early 1980's. This mod allows to freely spread all six voices in the Stereo panorama whilst having the original Mono signal available at its original phone jack (!). Actually this was the first commercially available synthesizer to implement MIDI! The Japanese counterpart was Roland's Jupiter 6, another great synthesizer which I like very much.
Musikding's Panorama 600 Pan Mod kit includes all necessary parts to enable a smooth assembly of the PCB and its integration into the synth. It takes a couple of hours to get the job done but it's r e a l l y worth it.