The ion project is an effort to provide a very simple but powerful content management system based on the most recents technologies. Ion is 100% compliant with J2EE standards, uses XML to define contents structures, XSL to provide rendered contents in many format (HTML, XML, PDF, TXT, ...), and JSP with JSTL as a template system.
You can use ion as an opensource content management framework to help you building your own CMS application, or either use the ion content server as an out of box product to build your web site. ion is perfect to build corporate web site where many actors should write, review and publish some content.
The ion project uses a lot of good open source components from apache, opensymphony and exolab.