Django source-code repository, wiki and bug-report system
Django is available open-source under the BSD license.
Getting the code
Django uses Subversion (svn) for managing its code.
Assuming you have Subversion installed, the following command in a terminal will fetch the most recent code for you:
svn co http://code.djangoproject.com/svn/django/trunk/
Django also offers "official" release tarballs at the download page.
Browsing the code online
Before anything, please read How to contribute to Django. You'll find out how the Django community works, and possibly save yourself much grief in the future. :)