Concrete
From Organic Design wiki
I've been introduced to another CMS yesterday by a guy I used to do some PHP work for a few years back. It's called Concrete. I was talking with some of the bro's about CMS's and saying the best one I knew for simplicity of use that was free and open was Wordpress, but Andrew said he'd found Concrete to be much better for end-users. It's still built on PHP/MySQL so I could install a version on our server quite easily.