This isn’t for the faint of heart, but Fink brings the world of open source to your Mac. Specifically, it allows you to pick from among hundreds of software packages that have been “ported” to Mac OS X from UNIX and Linux.
Linux operating systems usually offer some sort of package management command such “apt-get” or “yum”. Fink provides this same functionality for Mac OS X users in Terminal. You could use Fink to install MySQL, PostgreSQL, gnuplot, amaya, and more.