What's the Java EE killer apps?

Java EE 6 and JSF 2.0 has been released, as also Spring Frameworks 3.0. But when I think of killer apps what comes to my mind are: WordPress, Drupal, Magento, Moodle, vTiger CRM.

What are the Java EE killer apps, specifically the open source opens?

I definitely can think of a few well-known open source Java apps, like Liferay, Alfresco, Nuxeo...

These definitely aren't lightweight. And they're not (yet?) using the latest improvements available in Java as of 2010, not even 2009. And I shudder to think these apps being used as the reference best practices or study of Java EE's ease of development.

Can you suggest Java EE apps that are...

• "killer app" compliant, i.e. highly useful
• demonstrating practical usage of the latest Java EE technologies
• can serve as a learning tool, reading Java EE code shouldn't be that hard
• using the best design & programming practices of the Java EE community
  
• open source (hopefully)

Any ideas would be much appreciated!