Open Educational Resources (OER's) are teaching, learning, and research resources that are free of cost and access barriers, and which also carry legal permission for open use. (SPARC)
Mason OER Metafinder (MOM)
MOM is the "Google for OERs" because it simultaneously searches across the obvious OER repositories (e.g., MERLOT II, OAOpen.org, OER Commons, OpenStax CNX, etc.) but also sites like HathiTrust (full-view materials only), DPLA, OERs at Internet Archive, and Project Gutenberg.