You can download this book’s source code by using the git version control system. An OS X implementation of git is available at http://code.google.com/p/git-osx-installer. OS X git implementations include both command-line and GUI solutions, so hunt around for the version that best suits your development needs.
There are third-party git tools, as well—some free and some not. These are two of the most popular:
SourceTree—A free git hub client tool available at www.sourcetreeapp.com
Tower—A paid client with a polished UI at www.git-tower.com ...