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 52 different sources and contains 155,375 records.
"Open textbooks are textbooks that have been funded, published, and licensed to be freely used, adapted, and distributed. These books have been reviewed by faculty from a variety of colleges and universities to assess their quality."
Organized by the Open Education Network, based in the Center for Open Education at the University of Minnesota. Art history resources are interspersed with other arts content in the arts section, and include titles like American Encounters (2018), The Bright Continent: African Art History (2018), and Guide to Byzantine Art (2021), to name a few. Utilizes Creative Commons licenses, as most OER do.