The comment of 'Shreyas Satish' led me to the rails guides on my harddisk. I had only to build it.
After installing Ruby (1.8) on Ubuntu:
sudo gem install rails
sudo apt-get install ruby1.8-dev # required for RedCloth
sudo gem install RedCloth
sudo ruby /var/lib/gems/1.8/gems/railties-3.0.7/guides/rails_guides.rb
then browse to:
file:///var/lib/gems/1.8/gems/railties-3.0.7/guides/output/index.html
