git

SourceTree

SourceTree is a free Mercurial and Git Client for Windows and Mac that provides a graphical interface for your Hg and Git repositories.

Git

Git is a free and open source distributed version control system designed to handle everything from small to very large projects with speed and efficiency.  Git is easy to learn and has a tiny footprint with lightning fast performance. It outclasses SCM tools like Subversion, CVS, Perforce, and ClearCase with features like cheap local branching, convenient staging areas, and multiple workflows.

GitHub

GIT version control repository hosting service.  How people build software.  Millions of developers use GitHub to build personal projects, support their businesses, and work together on open source technologies.  GitHub fosters a fast, flexible, and collaborative development process that lets you work on your own or with others.