Digital Public Library Broad coverage of general and scholarly resources available.
Online Books Page University of Pennsylvania searchable...3 million free books online
Open Access Digital Theological Library Scholarly journals, articles, and some eBooks on a variety of subjects in addition to theological resources.
Open Access Textbooks complete textbooks are available. Search by subject or title categories.
Directory of Open Access Journals A general subject list of open access journal articles.
Faith and Philosophy : Journal of the Society of Christian Philosophers Asbury University's Open Access Journal...free access.
LibreTexts another site for free, completely online textbooks in many of the fields of undergraduate studies. An interesting feature are the videos and 3D displays to add to learning the material.
The Open Library...Books indicated by "borrow" are available. This is a division of the Internet Archive.