Php Framework Or Cms Based On Good Framework - Multi Site

[GregInChrist]

I am looking for a cms that can support multiple sites, rather I would like to just be able to have a library of cms files that all(or most) of the sites that I build could draw from. I would like all my customers to be able to use a cms without adding 1000 plus files per-site. I would like something that is oop for extensibility. Does anyone know of a good cms that would fit this criteria? Otherwise what would you consider to be the best oop php framework to use for such a task. I know the modx crew thinks of modx as a framework rather then a cms. This seams like it could be a good start because it is already set up as a cms not just a oop framework. Also one of the requirements would have to be a good permissions system. I would like to be able to edit and control all the sites from a central system and code base.