You can find githib of noobs (New Out Of Box Software), firmware, linux, userland (Source code for ARM side libraries for interfacing to Raspberry Pi GPU), target_fs, tools, and quake3.
As example, if you want to get a copy of the linux repository, enter the command:
$ git clone https://github.com/raspberrypi/linux
or enter the following command to clone fireware repository:
$ git clone https://github.com/raspberrypi/firmware
Git receives a copy of nearly all data that the server has. Every version of every file for the history of the project is pulled down when you run git clone. ~ reference: http://git-scm.com/book/en/Git-Basics-Getting-a-Git-Repository#Cloning-an-Existing-Repository