SIPF:
Simple Intelligent PHP Framework
Simeon Ivaylov Petrov Framework
SEO Ideological PHP Framework (SEO - Search Engine Optimization)

This is a base PHP framework for making simple websites with clean URLs.
It is absolutely free!
It's developed for advanced php web developers but if you are a beginner in php programming, I think you can also understand how does it work. SIPF is not a CMS (Content Management System) and it doesn't use the MVC (Model View Controller) logic as most of the PHP frameworks do.
I made it using my own logic and I think the final product that came out is very simple to understand and using it to develop your own website will be very easy, too.