I've had a lot of fun playing with Cockpit CMS.
It's a "An API-driven CMS without forcing you to make compromises in how you implement your site."

Its a CMS without a front end. The front end is completely up to you. This tool takes care of all the back-end stuff. It provides a UI for building content types, uploading media, editing media and content, doing site backups and authentication. How the data is displayed is entierly up to you.

Built with a custom microframework called "Lime" which looks alot like slim2 and a storage system called "Mongo lite", it provides everything you need to build small sites that are a joy to work with.

The documentation includes a walk-through on how to build a simple blog.