Openly Available Sources Integrated Search (OASIS) is a search tool that aims to make the discovery of open content easier. OASIS currently searches open content from 117 different sources and contains 388,707 records.
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:
Provision of openly licensed textbooks and other OER materials with a broad discipline focus including; business, education, science and mathematics
Provides college-level open textbooks from higher education institutions around the world.
Initiated by Rice University, their free textbooks are developed and peer-reviewed to ensure they meet the scope and sequence requirements of college courses.
Created by the University of Minnesota to support development of high-quality open textbooks in various subjects.