This is an open discussion group on US politics that anyone can join and where messages from new members are moderated.
I found it quite difficult to find open groups really- many that interest me seem to be closed. I wonder if the Blog is taking over from the open discussion group.
I do notice though that webpages such as the e-portfolio page will often have what amounts to a discussion for people who are trying technical things in the application.
Also the Communities in platforms such as the AkoAotearoa one must surely be discussion groups.