Mason OER Metafinder
The Mason OER Metafinder is a discovery tool from George Mason University Libraries. Unlike other open educational resource sites, it does not search a static catalogue. Instead it runs a real-time simultaneous search across 21 different sources of open educational materials and returns results as they arrive.
Treat it as a way to locate open educational resources across many repositories at once, a starting point for finding content to ingest rather than a dataset you can download in bulk.
Related sources
LibreTexts
One of the largest open textbook platforms, covering higher education with some K-12 material. Hosts interlinked textbooks and reference material across science, mathematics, humanities, and social sciences. Mostly NonCommercial, so commercial use is ruled out.
MERLOT
A curated collection of online learning and support materials, plus content-creation tools, led by an international community of educators, learners, and researchers. Points to resources hosted elsewhere across many disciplines.
MIT OpenCourseWare
Teaching materials from more than 2,500 MIT undergraduate and graduate courses, published freely online. Includes lecture notes, assignments, and exams. Released under a NonCommercial licence, so it is free to use for non-commercial purposes only.
OER Commons
A digital library of over 500,000 open educational resources gathered from institutions around the world. Aggregates full courses, modules, lesson plans, videos, simulations, and assessments across every discipline and education level.