Building Joomla Templates
Here are two extremely basic lightweight templates that are intended to be used as a framework to start building your own custom Joomla! templates without the restrictions of commercial templates. Each has an in depth guide that fully explains what makes the framework tick.
The Three File Template
Possibly the smallest Joomla template ever! This guide aims to teach you the very bare essentials needed to build your very own template. It has in-depth coverage of the code used in the three most essential template files and introduces concepts that are covered in more depth in the HD-Framework guide.
A lightweight template, ideal to be used as a framework to build your own custom templates from the bottom up. It is recommended you read the Three File Template guide beforehand as this guide does not repeat details of the coding that is already covered there.