JTalks.org is an open source project developed by JavaTalks community. JTalks includes several sub-projects which include forum, articles, blog, webinar components, and so on.
More information about JTalks.org is here.
I took part in two iterations of the project. During the first one I was developing a simple UI for admin panel that enables user to manage different subresources such as forum, article, etc. In the second iteration I implemented backend functionality for managing forum's branches.