SiteMesh is a lightweight and flexible web application framework that applies the Gang of Four decorator pattern to allow a clean separation of content from presentation.
Imagine working with only the simple content of your website and having the complex presentation code applied (decorated) just before delivery to the browser.
SiteMesh is easy to learn. 5 minutes to setup, and 10 minutes to start being useful. At the same time, SiteMesh is has many advanced features and works with popular frameworks such as Spring and Struts.
SiteMesh may be simple to start using right away, but there is much more,
For more details, see Mike Cannon-Brookes' PowerPoint presented at the Vegas Server Side Symposium.