Hunting for simple CMSes is quite a task. If you do a search over the internet for CMS, all the results are mostly heavy industrial cmses. As flatfiles, xml or SQLite database types become popular, we wonder why no such CMSes based on files exist. In fact, they do. GetSimpleCMS and WolfCMS, are 2 of many.
After a few months of testing. We stuck to GetSimpleCMS. Easy and quick to work with. http://get-simple.info/