Web Access
http://svn.boo.codehaus.org/ provides a web interface for browsing the source code currently in SVN.
Anonymous Subversion Access
The code of the project can be checked out by anyone through anonymous svnserve access with the following command:
svn co http://svn.codehaus.org/boo/boo/trunk
Notice however that this will get the latest development bits and some of the test cases might fail. However if you want to work with the most up to minute version, this is what you will need to check out.
If you want to track the development but don't care about the latest bits (and the possible failures) check out svn://svn.boo.codehaus.org/boo/scm/boo/branches/stable/ instead:
svn co http://svn.codehaus.org/boo/boo/branches/stable
Developer Subversion Access
svn co https://YOUR_USERNAME_HERE@svn.codehaus.org/boo/boo/trunk
Git SVN
If you prefer, you can use Git to track Boo subversion repository. A bootstrap git repository is available, checkout Boo's Git page for details.
Git allows you to work offline, create your own local branches you can commit on etc..