Developed by the Institute for the Future of the Book, 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.” (CommentPress home page)
Starter Links: CommentPress home page | Institute for the Future of the Book | Examples of CommentPress in action