Here is a quick list of apps that I frequently use on OS X. I believe all of them are free and open source. many of the applications are development tools that I find useful.
The Gimp – graphics editing program that requires X11
Platypus – packages python/perl/php/shell scripts as double-clickable OS X applications.
Those are my favorite, most used apps. You should also check out this list of mac apps, some of which I’ve used either on the mac or other platforms, others I plan on trying soon.
