This framework is currently being built by Matt Sparks. The entire process is being documented.
Building a PHP Framework: Part 1 - Why? Seriously, Why?
Building a PHP Framework: Part 2 - What is a Web Framework?
Building a PHP Framework: Part 3 - Time For Action
Building a PHP Framework: Part 4 - The Foundation
Building a PHP Framework: Part 5 - Test Driven Development
Be sure to follow along on Twitter – @DevelopmentMatt.