Custom Meta Boxes is a framework for easily adding custom fields to the WordPress post edit page.
It includes several field types including WYSIWYG, media upload and dates. It also supports repeatable and grouped fields.
This project is aimed at developers and is easily extended and customized. It takes a highly modular, Object Orientated approach, with each field as an extension of the CMB_Field abstract class.
The framework also features a basic layout engine for fields, allowing you to align fields to a simple 12 column grid.