MacPorts for Mac

From MacPorts:

The aim of the MacPorts project is to develop a second-generation system for the building, installation and management of third party software.

MacPorts is probably best described by comparison: It's sort of like the FreeBSD ports collection or Fink in that it automates the process of building third party software for Mac OS X. MacPorts also tracks all dependency information for a given piece of software. In other words, it knows what it needs to build and install and in what order for the piece of software you want to work properly. MacPorts knows how to make, build and install the software to a specific location, meaning that software installed via MacPorts doesn't simply scatter itself all over the system or require user knowledge of dependencies in what order.