You can browse the source tree directly via http://acegisecurity.svn.sourceforge.net/viewvc/acegisecurity/

The code can be checked out anonymously with the following command:

svn co http://acegisecurity.svn.sourceforge.net/svnroot/acegisecurity/spring-security/trunk/

If you'd prefer not to use subversion directly, please see our downloads page for nightly snapshots.