Git is a distributed source version control system.
Git is free software and is used for everything in the contribution process: code, image, models, sound files, everything is tracked in git repositories. We also do heavy usage of git submodules. Some of our tools expect git to be present and data to actually be stored in repositories to work properly.
The Git website is git-scm.com.
The Git documentation can be found on git-scm.com/doc.
The Git source repository is github.com/git/git.
See Source code for details.
If you already have Git installed, you can skip this step.
Apple has included Git with Xcode since version 4. You may download Xcode from Apple's developer website. Please note that while XCode 4 was available for a very brief time for 32-bit and Snow Leopard users for a small price ($5 from the Mac App Store), this is no longer the case; it is now free, but available only to 64-bit Lion users. Snow Leopard (10.6) users and prior may now only use XCode 3, which does not include Git. If you are one of these users, you may acquire a copy of Git from its site. A selection of GUIs for Git is also available.
Debian and Ubuntu
Install Git using the package manager:
$ sudo apt-get install git