Rattail Development Guide
So you're tired of reading, and ready to code. Sorry, more reading first.
This guide assumes you are either wanting to create a new app based on Rattail, or else you wish to modify an existing one. In either case the app is assumed to be "custom" in some way and the examples in this guide will use the name "Poser" to refer to this custom app.
You are strongly encouraged to familiarize yourself with the Admin Guide before tackling development.
The Big Tour
This is also linked from the Concept Guide but it deserves a link here too.
Please see The Big Tour for a basic technical overview of the possible features / components of a Rattail/Poser system.
Also unfinished, but a good start nonetheless, is the Rattail Tutorial. This walks you through the process of getting a new project up and running.
Writing this Dev Guide may take a while to get right. In the meantime see this collection of Lil' Snippets which is sort of the staging area for new dev docs.