Digitech mosaic
This pedal may be very limited in its application but that is not necessarily a bad thing. If you are a guitar player that occasionally wished they could coax a realistic 12 string sound from your electric or amplified acoustic guitar the DigiTech® Mosaic Polyphonic 12-String effect pedal might be just the thing you’ve been looking for.

“mediately identifiable 12-string tones are now yours with octave low strings and doubled high strings. Single notes and full chordal strums shine with polyphonic richness and celestial movement that will inspire you. The Mosaic’s balanced low-end response with crisp octave shimmer produces a tone that’s lush and articulate, just as with a 12-string guitar.”

For more info - http://digitech.com/en-US/products/mosaic.