Not just textbooks, which it targets, but also non-fiction (assuming the Boundless plan for monetizing the site works):
What Boundless does is to map open source content to chapters and sections of dominant textbooks. Students can enter the name of the assigned textbook on Boundless site, and the site automatically creates an aligned web based textbook (that is also totally free).
4 Thoughts About Boundless, Publishers, and the Lawsuit | Inside Higher Ed
If publishers and booksellers haven’t gotten around to rethinking their business models, they’d better get started.