The Scout Portal Toolkit (SPT) is a turnkey software package that allows groups or organizations who have collections of knowledge or resources they want to share via the Web to put that collection online without a big investment in technical resources. It includes keyword and fielded search engines, a recommender system, a metadata editor, user agents (push technology to notify users of new resources), forums (bulletin boards), resource quality ratings, resource annotations by users, and support for multiple dynamic user interfaces, selectable on a per-user basis.
Seir Anphin is a CMS focused on developing communities. Its core is a versatile platform for building any kind of site, but there is also a set of modules which provide features for building social networking hubs and communities. These modules integrate themselves during installation automatically, so you can just choose the features you need: forums, blogs, events calendar, file sharing, image gallery, and advanced article publishing.
WCN:Talk (originally called "FutureForum") is a Web discussion forum written in Perl and MySQL. It has many options, including message selection and sorting on the top index page. It also has collapsible branches, a menu that toggles between 'no menu', 'simple', and 'advanced' modes, full text search capability, the ability to send email to the admin and original poster, and many other features. It includes password protection, HTML templates, file uploads, message subscription, multiple discussion sections, and a lot more.