There are many opensource CMS product downloadable on the Internet. However there are only a few java based downloads. In this article, I will reference a few of the products and as time passes, I will try to write a quick review on them as well.
The old ARS Digita product now sponsored by Redhat and calledCCM
OpenCMS but be careful with this one. for a while all their documentation was in German ;-).
Cofax which is a neat little CMS, mainly for a heavy publishing site
MMBase
Leyna from Apache