eCampusOntario provides a curated collection of over 550 of the best open textbooks from other sources. Most book pages include comprehensive reviews by Canadian professors. There is also a guide to finding open textbooks.
MERLOT (Multimedia Educational Resource for Learning and Online Teaching) is a curated collection of Open Educational Resources, including textbooks. Many books include peer reviews, user reviews, or editor reviews. Users can restrict search results to textbooks only by selecting the appropriate material type. MERLOT is a program of the California State University system.
OER Commons is a large repository for Open Educational Resources, including textbooks. It is a product of the Institute for the Study of Knowledge Management in Education. Unlike some sources, OER Commons contains material for grade levels from preschool to graduate school and adult education. Textbooks are not generally as extensively reviewed as they are in other sources.
Open Textbook Library is a collection of open textbooks on a variety of subjects created by the University of Minnesota. This collection lists more books than the BC OpenCampus project, but fewer books are reviewed.
OpenStax College is a nonprofit organization and initiative of Rice University dedicated to publishing quality Open Access Textbooks. 15 titles have currently been published, and many have received positive reviews from professors on BC OpenCampus and Open Textbook Library.
Wikibooks is a huge Open Textbook project with over 2800 titles. Books are not officially peer-reviewed, and beyond the project's featured books there is little on-site means of evaluation. Many books are only partially complete.
A site listing free online computer science, engineering, and programming books, textbooks, and lecture notes. Books are published under open licenses, are in the public domain, or have another license that allows the work to be distributed freely.