It’s an RDoc template tailored to look better in the iPhone web browser (no frames, a lot less styling, native app feel thanks to iUI library, etc.).
Yup, the aforementioned iUI library code.google.com/p/iui/
Download it then write yourself a Rake task like the one provided (changing the appropriate paths, of course).
For the sake of simplicity, I removed the source code links and embedding.
I referred to the following projects when I got lost and confused:
github.com/rails/rails/tree/master/doc/template/horo.rb
github.com/mislav/hanna/tree/master
I borrowed CSS and some graphics from: