Possible mentor: Unknown
This is a system that hosts patches for the PHP project. An example usage is someone posts a patch to a mailing list, and instead of using a random server or pastebin they use this system at php.net to store and archive the patches. Likely related features would be added to enhance the archival and author experience. Experimental patches could also be stored here, although SVN is another option for that (perhaps both, as svn.php.net would probably be the storage backend for this patch server).
In related news, once upon a time Zend hosted a “PAT Directory” so patches wouldn't be forgotten.