This screencast made by Zope core developer Philipp von Weitershausen shows how to make a simple todo web application using the new Grok library for Zope 3. Grok alleviates the lack of agility in Zope 3 development by reducing the amount of configuration to a minimum and relying on conventions and short, convenient spellings instead.
Note that this screencast is about an older version of Grok. Some details have changed since (for example, Grok developers no longer need to touch any ZCML).
More information about Grok at http://grok.zope.org.