GetSimple CMS: They claim: “The Simplest Content Management System. Ever.”
And I would have to agree. After downloading the code it was up and running in a matter of minutes. Very impressed with the ease of installer, and the ease of customization.
On other flat file CMS I used the Atom Editor to do custom tweaks of the templates. No need for any additional tools here. If you know just a little about HTML and CSS the admin interface allows you to very easily customize the look and feel.
GetSimple CMS is so easy to install, easy to modify the template to customize the look and feel, it's hard to justify using something else for a very simple blog.