Grok is an extension to Zope 3 that makes it quicker and easier to develop web applications with Zope 3.  It is a web application framework for Python developers. Grok builds on existing Zope 3 technology like the component architecture but exposes it in a different way to the developer; making developing with Zope 3 more fun.

If you're a developer and haven't tried Zope 3 yet.  The Grok tutorial gives you an easy entry point to Zope 3 technologies.