BuddyPress is a suite of WordPress plugins and themes which extends WordPress MU and brings social networking features to a new or existing installation.
WordTwit is a plugin that utilizes the Twitter API to automatically push a published post to your Twitter account as a tweet, using the blog domain as a short URL.
CommentPress is an open source theme for the WordPress blogging engine that allows readers to comment paragraph by paragraph in the margins of a text. Annotate, gloss, workshop, debate: with CommentPress you can do all of these things on a finer-grained level, turning a document into a conversation. It can be applied to a fixed document (paper/essay/book etc.) or to a running blog.
Displays a book's cover image, title, author, links, and other book data from Open Library. OpenBook is for book reviewers, book bloggers, library webmasters, anyone who wants to put book covers and data on their WordPress blog or website. Use the OpenBook button in the WordPress visual editor or insert an OpenBook 'shortcode' with a book number in a WordPress post, page or widget. OpenBook will display a book cover image, author, and other book data from Open Library (http://openlibrary.org). It also displays links to book websites. Users can control the content and styling through templates. OpenBook inserts COinS to integrate with applications like Zotero. Librarians can point OpenBook to their library records using an OpenURL resolver. Requirements. To use OpenBook, your server must use PHP 5 or higher, and cURL must be enabled.