When I was 17 and still in school I became fascinated with fractals and especially the Mandelbrot
set. One day late at night when I couldn't fall asleep I started to code a software to visualize
and explore fractals. Over the next year this grew into jFractal, the first "serious" Mac app I
ever made. It can natively render the Mandelbrot set, the Julia set and the Burning Ship Fractal.
You can easily customize the color mapping.
The picture above image was made with jFractal.