It lets you use the computer itself as a musical instrument, played by moving the mouse with one hand while you control dozens of available musical parameters from the Mac's "qwerty". It's a great musical idea generator, ear trainer, compositional tools, and improvising instrument. The software does a lot of harmony handling for you (you control the variables it uses for this), so it's useful - as are all "real instruments"at any level of musical training, experience, or skill, from beginning through professional.