Possibly the most widely adopted open textbook repository for higher education .
BC Open Textbook Project (British Columbia)
Boundless provides a number of open course packages. Each one contains reading materials, PowerPoints, and assessments.
Find Free Course Materials Related to a Book from Calstate
College Open Textbooks is NOT a content provider. Instead, they search available open textbooks and provide the links. Currently, they are tracking more than 100 open textbooks for use in community college courses.
Provides open educational resources (OER) and low-cost course materials that replace expensive textbooks.
Provides an academic-friendly publishing model and infrastructure which supports faculty adoption, remixing, and creation of open educational resources (OER) and courses.
These textbooks have proven quality and have been already used in classes at a huge number of universities and colleges. All textbooks are completely open with no strings attached.
It calls itself a "Store," but they are not a publisher. Open TextBook Store provides freely and openly available math textbooks created by Washington CTC faculty.
The Washington 45 are "courses selected from within the general education categories... at a public community, technical, four-year college or university in Washington state that will be able to transfer and apply a maximum of 45 quarter credits toward general education requirement(s)
Source: "Textbooks" by Open Washington: Open Educational Resources Network is licensed under CC BY 4.0