If you want to be brave, feel free to check out the latest version of CMS from the Subversion repository. You can do this from a shell with the following command:
svn co http://svn.cmsmadesimple.org/cms/trunk
This is a fairly dynamic piece of software that is updated frequently so if you using SVN please be aware that things can and will change and you might even lose some information. That's just the way it works.
You can also browse the source in SVN from your browser here