Please read for an updated status on RailsCasts:
Learn more or hide this
GitHub User: robinboening
The alchemy guide you mentioned is old. Bad that this one is still online, but you can find the actual guide here: http://guides.alchemy-cms.com/creating_modules.html
Since Rails3.1 and mountable engines, this is also implemented.
Alchemy is not only a CMS, its a framework for storing and rendering content.
You first have to understand the architecture behind it, but then its really flexible and comfortable for the user.
Have you ever tried Alchemy?
All these CMS (with a page model and a body column) out there are missing one big thing:
A flexible content storing architecture.
I would never give one big editor for managing the texts, formattings, images to my client. The client always breaks the layout, because of too many possibilities.
Take a look at http://alchemy-cms.com - its architecture is completly different and the usage is enduser-centric ;-)