Giving an accurate definition of a fractal is not really easy, but for the purpose of this projects it enough to say that a fractal is an image with infinite depth. That means you can zoom into it and will always continue to unfold its structure.
Nutria is basically a gallery of fractals and it contains a convenient tool to explore such fractals.
Fractals usually have a lot of parameters. Nutria allows you to try out new configurations for these parameters which might yield completely new images.
The current development state can be accessed at heroku.