SVN. It actually won via a killer library/app - TortoiseSVN.
But it was cleaned up, and mostly incompatible - after all all the commands had changed from cvs to svn :)
A cleaned up PHP would be interesting but it would need a truly killer app. Basically make a PHP clone except for the bad parts. I'd say that the killer app would be a very to use framework that provided various security best practices already built in.
And a PHP clone would need a 0 installation process - no messing around with shell commands or root access. Just copy your .phpclone files and you're set to go.
