LibreTexts
LibreTexts is one of the largest open textbook platforms, covering higher education with some K-12 material. It hosts interlinked textbooks and reference material across science, mathematics, humanities, and social sciences, organised so that related concepts link to one another.
Most content is released under a Creative Commons Attribution-NonCommercial-ShareAlike licence. You can freely use and adapt it for non-commercial purposes if you credit the source and share your derivatives under the same terms. The NonCommercial clause rules it out for commercial products.
Related sources
Mason OER Metafinder
A discovery tool that runs a real-time simultaneous search across 21 different sources of open educational materials, rather than searching a static database. Useful for finding content to ingest, not a dataset in itself.
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.