Via @georgwaechter I have come across SimPCoRe which is a content repository for PHP. Judging from the description and this discussion SimPCoRe does not fully implement JSR-170, but only a smaller feature set. It does, however, seem to implement the basic ideas and concepts of a (Java) content repository.
It is great to see the ideas and concepts of the "content repository" spreading - be it standards-based or an adaption/evolution or a minimal feature set. Anything that helps with the implementation of better content management systems is a good trend (see also this previous post). Especially, given the large amount of PHP-based CMSs I am happy to see more PHP developers working on content repository implementations (others are Jackalope and Flow3).