Harmony Box (aka JAEZZESiZER) is a synthesizer that has the rules of modal jazz built-in; you press a key, it plays the right chord. You just pick the key and the mode. An alias-free oscillator drives a self-oscillating filter and it has LFOs and Envelopes for fatness. It was created by Mike Massberg and Dave Gamble for Music Hack Day 2009.

Harmony Box is free and is available for Windows and Mac OS X in VST and AU instrument plug-in formats.