WordPress.org

Activity Streams - Global, personal and group activity streams with threaded commenting, direct posting, favoriting and @mentions. All with full RSS feeds and email notification support.

Extended Profiles - Fully editable rofile fields allow you to define the fields users can fill in to describe themselves. Tailor profile fields to suit your audience.

Extensible Groups - Powerful public, private or hidden groups allow your users to break the discussion down into specific topics. Extend groups with your own custom features using the group extension API.

Friend Connections - Let your users make connections so they can track the activity of others, or filter on only those users they care about the most.

Private Messaging - Private messaging will allow your users to talk to each other directly and in private. Not just limited to one-on-one discussions, your users can send messages to multiple recipients.

Discussion Forums - Full powered discussion forums built directly into groups allow for more conventional in-depth conversations.

WordPress Blogging - Allow your users to start their own WordPress sites (using WordPress's Multisite feature), and track posts and comments from across your blog network in the activity stream.

User Settings - Give your users complete control over profile and notification settings. Settings are fully integrated into your theme, and can be disabled by the administrator.