Redmonk calls Conversant "the most powerful groupware/cms I've ever worked with." I'm boggled (but pleased) by the fact that it comes with an NNTP (i.e. Usenet) server. That's a strange bit of interconnectivty I wouldn't expect at all from the product.
Conversant was designed, if I understand correctly, in part using Jon Udell's Practical Internet Groupware. I hardly use the NNTP interface at all but some people swear by it. It's certainly the best interface for dealing with threaded discussions when you need to catch up very quickly.