Today the main PHP development branch has moved to the git version control system. In the past, PHP has been developed on cvs and svn. The move to git is very common these days. Git is, for example, the version control system used by the linux kernel developers and the Horde Application Framework.
PHP uses the github infrastructure for the public repository, which currently holds 52 branches. It will be interesting to see how they will convert their commit email script to git.
The public PHP git repository is available under http://github.com/php/php-src