In the words of EarthQuaker Devices:

The Arpanoid takes whatever you play and transforms it into an adjustable ascending or descending scale. It features 8 intuitive and expandable modes and will work on complex chords as well as single notes in any key. The Arpanoid has an all analog dry signal, all digital wet signal and true bypass switching. Like all EarthQuaker Devices pedals, this dude is handmade one at a time in sunny Akron Ohio.