University of Michigan Press- Areas of particular focus are performing arts; classical studies; political science; American studies (especially disability and class studies); Asian and African studies. They created a document that lists presses that have made their e-books openly available during this time. Go to the link, a PDF file.
Directory of Open Access Books- A service of OAPEN Foundation based at the National Library in The Hague. Database contains more than 5,000 academic, peer-reviewed books from 163 publishers.
National Academies Press Free eBooks Created by the National Academy of Sciences to publish the reports of the National Academies of Sciences, Engineering and Medicine with more than 8,500 titles in PDF format.
NCBI Bookshelf- Provides free online access to books and documents in life science and healthcare.
OAPEN Library- Open Access Publishing in European Networks (OAPEN) Library contains freely accessible academic books, mainly in the area of humanities and social sciences.
Open Book Publishers- Founded in 2008 by a small group of academics at the University of Cambridge, Open Book Publishers publishes monographs and textbooks in the Humanities and Social Sciences.
World Digital Library- Project of the U.S. Library of Congress and UNESCO. Makes available on the Internet and in multilingual format, significant primary materials from all countries and cultures.
MuseOpen- Open access ebooks through Project Muse in the humanities, social sciences, and sciences.
JSTOR- Open Access ebooks are available on JSTOR at no cost to libraries or users. More than 6,000 titles are now available from respected presses, such as University of California Press, University of Michigan Press, and the RAND Corporation, and the collection continues to grow.
Internet Book Archive- Offers over 12,000,000 freely downloadable books and texts. There is also a collection of 550,000 modern eBooks that may be borrowed by anyone with a free archive.org account..
Online Books Page- the University of Pennsylvania indexes over 1 million books available on the web, including those fromProject Guttenberg and the Hathi Trust Digital Library.These ebooks can be downloaded to your desk or laptop and those in Project Gutenberg can be downloaded to your Kindle, Android, iOS or other portable device.