In Knowledge Unlatched’s funding model, libraries jointly fund books from publishers to make them open access. If not enough libraries come together to support the project, only some of the titles will be made openly accessible. However, the participating institutions will in any case receive free and permanent access even to the titles that are not later openly accessible.
The focus and beginning of the Open Access movement has always been more on journals and journal articles. In the meantime, however, there are not only books on the subject of openness. More and more books are published Open Access.
Many classical publishers – such as Springer or transcript – also have a large number of books published in Open Access. The variety of business models is constantly growing, as is the case with the publication of journals (essays). Here, too, Open Access costs money.
Example of a book on Open Access that is unfortunately not available: Open Divide : Critical Studies on Open Access / Ulrich Herb; Joachim Schöpfel (eds.) 2018. Litwin Books, LLC. After all, there is a collection of the article preprints of this volume here.