Pods Export to Code plugin that lets you export your Pods configs to PHP
The Simple PHP Framework
Open Source PHP Framework (originally from EllisLab)
Quite possibly the smallest MVC framework you'll ever use.
The core of the FuelPHP framework
A micro PHP framework that's fast, easy, clean and RESTful. The framework does not do a lot of magic under the hood. It is, by design, very simple and very powerful.
Slim is a PHP micro framework that helps you quickly write simple yet powerful web applications and APIs.
PHP Framework Benchmark