To access MMBase's Subversion repository anonymously you must of course have svn installed.
The URL is: https://scm.mmbase.org/
It can be used on the command line:

svn co https://scm.mmbase.org/mmbase/trunk

for guest access but when you want to check in, svn will request a name and password. MMBase developers or committers can use their original CVS pserver account. Otherwise contact the developers-list and we'll help you.
The history of our repository can be browsed at http://scm.mmbase.org/view/