As part of PeopleAggregator's auto-update system, I started on a stripped-down Subversion client in PHP. Currently it's capable of sending a REPORT command to a Subversion server, requesting a diff from a given revision to the latest version, and parsing and applying the diff. All in PHP - depending only on HTTP::Request and Net::Socket from PEAR (and PHP5, I guess).
This is pretty much all we need, although it would be kinda cool if it could also read/write .svn folders, which would make it interoperable with the real svn client. Is anyone interested in doing this work? I'm thinking we'll start by putting everything in MySQL, but perhaps using .svn folders would make more sense, as then we can use this to bootstrap an install, later on.