Free to use and download textbook site supported by the Center for Open Education and the Open Textbook Network. Subjects include Accounting, Business, Education, Humanities, Mathematics, Social Sciences, and more.
MIT OpenCourseWare makes the materials used in the teaching of almost all of MIT's subjects available on the Web, free of charge. More than 2,400 courses are available and are licensed under the CC By-NC-SA 4.0 license
OASIS (Openly Available Sources Integrated Search)
OASIS searches for open content from over 75 different sources. It is created and managed by SUNY Geneseo's Milne Library.
This site is a collected, searchable database of all things OER. The collection is built from an initiative of the UNESCO/COL Chair in OER at Athabasca University and the UNESCO Chair in OER at the Open University of the Netherlands.
A global non-profit network promoting open education worldwide. This site houses links to OER textbooks, information about how to become involved in OER efforts, provides news and webinars for OER supporters.