That's true http://www.exoplatform.com/ has a forum portlet in its Knowledge Suite.
It is currently being actively ported to GateIn an also works on Tomcat. You can even play with it here : http://ks.demo.exoplatform.org
That said, it is currently not shipped with GateIn but will be a separate extension that you can deploy on top of it.
do you know if there is a timeline for when this extension will be available?
We were waiting for beta3 to make our extension available. Now that it's there, it's a matter of days until we make a public release.
I suggest you keep an eye on http://www.exoplatform.com/portal/public/website/community/forum for an announcement.