Open Source J2EE Components

I have been looking into the JIRA and Confluence products by Atlassian have found that most of the functionality is provided by a few open source components from OpenSymphony. OpenSymphony is an open source project that is developing a number of open source components to support the development of J2EE applications.

Components Provided
WebWork - MVC framework that stresses simplicity and interoperability.
OSWorkflow - Flexible workflow engine based on finite state machine concept.
Quartz - Job scheduling system.
SiteMesh - Page layout and decoration framework that cleanly separates content and presentation.
OSCache - Web-tier caching framework which enables massive speed increases and improved error tolerance.
OSCore - Set of utility-classes useful in any J2EE application.
XWork - Command pattern framework.
PropertySet - Typed properties storage framework.
Clickstream - Utility to track the current users on your site.

Links
OpenSymphony Home Page
JIRA Product Page
Confluence Product Page
Atlassian Home Page