XronoMorph, from Dynamic Tonality, is a free OS X and Windows app for creating multilayered rhythmic and melodic loops. Here's Dynamic Tonality's own description of it:

Each rhythmic layer is visualized as a polygon inscribed in a circle, and each polygon can be constructed according to two different mathematical principles: perfect balance and well-formedness (aka MOS). These principles generalize polyrhythms, additive, and Euclidean rhythms. Furthermore, rhythms can be smoothly morphed betweenc and irrational rhythms with no regular pulse can also be easily constructed.

Each polygon can play an independent sound, and XronoMorph comes with a useful selection of samples to play the rhythms. Alternatively, you can load your own VST or AU plugins, or send MIDI to an external software or hardware synth. The rhythmic loops can be saved as presets within XronoMorph; they can also be saved as Scala scale tuning files, which means XronoMorph can be used as a tool for designing well-formed (MOS) and perfectly balanced microtonal scales.

Pricing and Availability:
Free download.

More information:

• XronoMorph