The Institute for the Future of the Book has released version 1.0 of Sophie, an open source tool for creating and reading multimedia networked documents.
Here's an excerpt from the announcement:
Sophie is software for writing and reading rich media documents in a networked environment.
Sophie’s goal is to open up the world of multimedia authoring to a wide range of people and institutions and in so doing to redefine the notion of a book or "academic paper" to include both rich media and mechanisms for reader feedback and conversation in dynamic margins.
Read more about Sophie at "Sophie Project Gets $1 Million from Macarthur Foundation," the Sophie documentation, and the Sophie tutorials.