an online forum for a National industry information organisation. I used the discussion group facility in Microsoft FrontPage to do it, although I heavily customised the appearance and 'feel' of the standard Microsoft offering.
I can't give details, or a link to the site for client confidentiality reasons, but I can say that the forum was a place where senior executives of major companies in one of our biggest industries can exchange ideas and opinions on how to make the industry more efficient. My brief was to make the discussion area secure because the subject matter tends to be highly confidential, so I set up a workgroup on the organisation's Windows web server. Users get the NT authentication challenge when they try to enter the forum, and have to submit a username/password combination. This method is very secure, although it means manually setting up each user on the server. There aren't that many auhtorised users (about 200) and I get the server administrator to do it, as and when we need to add or remove someone
It all seems to work very well - at least the client appears to be pleased with it.