What is Harmonix?
Harmonix is a plugin for PhotoShop plugin compatible graphics applications. With Harmonix you can create complex harmonic wave forms with a high level of configurability and likewise quality.
Harmonix allows you to fully configure the first ten harmonic frequencies which is more than enough for most situations.

Who could use Harmonix?
The easiest answer would be "Everybody who wants to." and to be honest that's actually the answer I'll give you :)
Harmonix was created out of a personal need to visualize harmonic wave forms for my study and personal interest in sound. So far I've used it for just that but also for graphical work and such.

So, what does it actually do?
To fully understand what Harmonix does one should have at the very least a basic understanding of the superimposing of waves and harmonic frequencies. For the uninitiated I'll explain a bit.
Superimposing is basically another way of saying "adding up" within the context of this plugin (and in fact most programs that work with wave mixing).
Harmonix frequencies are basically frequencies which are a factor higher than the "base" frequency. The base frequency could be any random frequency.
The thought behind mixing these is the fact that it is possible to generate any wave form by simply creating harmonic wave forms. Most people will have heard of saw tooth and block forms, these too are easily created by mixing harmonics.
These are of course not perfect descriptions but to go in depth into these subjects would be unnecessary to say the least. If you'd like to know more about this then there are literally hundreds of books available that go in depth on this subject.

Cool! Now how do I get started?
Just follow the instructions on installing and you'll be off in minutes :)