On the negative, apt-get (combined with the obsessiveness of the debian policy manuals) is an amazing thing, few other operating systems can match apt-get for ease of installing software.
There are a couple of projects to provide open source software under OS X (fink and darwinports). However at least fink is amazingly annoying to use--the vast majority of times if you want to install something it'll pull in scores of dependencies. Not to mention it doesn't support intel macs that well yet.
So I dug out an old utility stow to manage my C packages. For my python packages I've tried to use Python Eggs.