"DOAJ is a community-curated list of open access journals and aims to be the starting point for all information searches for quality, peer-reviewed open access material." Covers all areas of science, technology, medicine, social science and humanities (About DOAJ).
"PLOS publishes a suite of peer-reviewed Open Access journals featuring quality research, expert commentary and critical analysis across all areas of science and medicine. Each journal is editorially independent and specialized with regard to both its selection criteria and breadth of content." (PLOS Journals).
DPLA provides access to digitzed books from American libraries such as the New York Public Library, University of Michigan, Harvard University, and the LIbrary of Congress. The Bookshelf catalog includes over 1.6 million items. Perform a search, and from a book detail page you’ll be redirected to a relevant website, where you can further read it online or download.
"digitalculturebooks is an imprint of the University of Michigan Press dedicated to publishing innovative work in new media studies and digital humanities." Available to view for free. Generally produced under an Attribution - No Derivative Works 3.0 Creative Commons License. (digitalcultlrebooks About Us).
"The OAPEN Library contains freely accessible academic books, mainly in the area of humanities and social sciences. OAPEN works with publishers to build a quality controlled collection of open access books, and provides services for publishers, libraries and research funders in the areas of deposit, quality assurance, dissemination, and digital preservation." (OAPEN LIbrary).