Wiki
GitHub-powered Netzke wiki is becoming the primary source of documentation, including basic and advanced topics around the Netzke framework, tutorials, guides, FAQ, etc. Feel free to contribute to it by editing and creating new pages (you'll need a GitHub account).
API
Generated RDocs for the Netzke gems can be found here.
Blog
In the WriteLessCode blog, you'll find several tutorials published over the past 2 years. Some of them are outdated, but the most interesting ones are being gradually moved over to the Wiki.