[Radiant] Examples for advanced radiant extensions ?

[Benjamin Heitmann]

Hello there.

I am currently looking into the radiant extension architecture, and I am 
very excited about the possibilities there.

But since there is no real documentation for writing extensions, I am 
searching for existing extensions to learn from them. So my question is:

Whats the most advanced current extension for Radiant ?

And: what kind of entities can an extension create ?

(I saw that I can create tabs in the admin interface, and I can create 
tags for using inside of a page. Is there one or many root objects, for 
the entities which an extension can create? Or any other guideline which 
defines what an extension can create?

I am currently looking at the mailer extension, but I cant get it to 
run, because it complains about an undefined variable.

Generating whole pages on the fly would by my primary interest for an 
extension.

To further elaborate on that: I want to investigate building a framework 
for semantic web applications using active rdf (for the semantic web 
data access part) and ruby on rails (for the web application interface 
part). Radiant would fit in nicely for the administration and the 
content managment aspects.

Sadly the vertical application slices approach of django, as described in
http://www.wiseheartdesign.com/2006/12/6/rails-needs-something-better-than-engines/
does currently not exist, and so I am looking into the possibilities of 
building a radiant extension.