Fractint was well respected software. It's very old but the source is available. I'm not sure what kind of licence the source is under - this was in the days when people called things "stone soup".

The math is going to be easily portable.

http://www.nahee.com/spanky/www/fractint/getting.html

http://www.fractalforums.com/ could be a start

This site has some useful articles: http://hpdz.net/TechInfo.htm