Here are a few online Netzke demo projects along with the source code.

"Official" demo

Some components shown in this demo accompany one of the tutorials (also here). Others just show what's possible. Make sure to check out the source code.

Yanit

Yanit - Yet Another (Netzke) Issue Tracker - is a demo application created for nomadcoder's talk at RubyShift 2011. The source code is at GitHub

Netzke Web Desktop

Paul Cockrell created an awesome prototype of a Netzke-driven web- desktop. The source code is at GitHub.