Open access books
In some disciplines, research findings are often published in books rather than journals. Until recently, there were very few open access options available for books. Partly, this was due to the high fixed costs associated with providing editorial support, proof-reading, and type-setting services to book authors. The diminishing market for books has also made scholarly book publishing a relatively high-risk activity; especially for commercial publishers.
Fortunately, if an author wants to disseminate an open access digital copy of their book (or is required to do so as a grant requirement), there are now a few options available.