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.
I bought a copy of David Weinberger's "The $100 Million Dollar Secret" on lulu.com and was delighted both with the book and the lulu experience. I'm shocked that it's sold so few copies. Clearly, e-books and download have a long way to go. The culture of "free" is indeed pervasive.