Mason OER Metafinder - The Mason OER Metafinder runs a simultaneous real-time federated search across 22 different OER sources.
OASIS - Openly Available Sources Integrated Search (OASIS) is a search tool that aims to makethe discovery of open content easier. OASIS currently searches open content from 117 different sources and contains 388,707 records.
Openstax College - Initiated by Rice University, their free textbooks are developed and peer-reviewed to ensure they meet college courses' scope and sequence requirements.
Open Textbook Library - Created by the University of Minnesota to support the development of high-quality open textbooks in various subjects.
CC Search - CC Search is a tool that allows openly licensed and public domain works to be discovered and used by everyone.
There are numerous OER textbook platforms available; some of the more well-known ones are:
BC Campus OpenEd - Provision of openly licensed textbooks and other OER materials with a broad discipline focus, including; business, education, science and mathematics
EdTech Books - Provision of openly licensed textbooks and other OER materials focusing on education as a discipline.
Lumen Learning - Lumen provides open courses in a variety of high-demand subjects and disciplines. These courses are collections of high-quality OER and may not necessarily be textbooks.
Merlot - A curated collection of free and open online teaching and learning services.
OER Commons - Provides college-level open textbooks from higher education institutions around the world.
Teaching Commons - The Teaching Commons showcases high-quality open educational resources from leading colleges and universities and makes them available to educators and students around the world.
The Big List (by format, discipline and more) curated by theLibrary of the University of Pittsburgh, USA
For Irish Higher Education resources, search the National Forum for Teaching and Learning's (NFTL) RESOURCE HUB (launched 2021).
Watch our short video on finding an open textbook and adding it to MyReadingList@TCD.ie (For academics) Finding and Adding an open textbook to MyReadingList@TCD.ie
This webinar (1:08 mins.) from California Community Colleges shows how to find and evaluate quality OER.
Take a look at these tutorials on searching different OER repositories (Mason OER metafinder, OpenStax (textbooks), OASIS, Open Textbook Library) from Jillian Maynard at the University of Hartford's guide: Getting started with OER: Tutorials - OER Repositories, with thanks.