Macports

MacPorts, formerly called DarwinPorts, is a package management system that simplifies the installation of software on the Mac OS X and Darwin operating systems. It is a free/open source software project to simplify installation of other free/open source software. Similar in aim and function to Fink and the BSDs' ports collections, DarwinPorts was started in 2002 as part of the OpenDarwin project, with the involvement of a number of Apple Inc. employees including Landon Fuller, Kevin Van Vechten, and Jordan Hubbard.
It allows the installation of a number of packages by simply entering the command in the Terminal, which will then download, compile and install the requested software, while also installing any required dependencies automatically.