Libretexts

Open Library

openlibrary.org

Open LMS

openlms.net

MIT Open Library

openlearning.mit.edu

MIT OpenCourseWare

ocw.mit.edu

JSTOR

jstor.org

Wikisource

wikisource.org

Wiley Online Library

onlinelibrary.wiley.com

OpenStax

openstax.org

Wikiversity

wikiversity.org

Wikibooks

wikibooks.org

ProQuest

proquest.com

CORE

core.ac.uk

Crossref

crossref.org

OA.mg

oa.mg

Kortext

kortext.com

I, Librarian

i-librarian.net

Sage

sagepub.com

Econlib

econlib.org

OpenLearning

openlearning.com

Hindawi

hindawi.com

Libraries

libraries.io

LibKey

libkey.io

Mentes Liberadas

mentesliberadas.com

OpenCurriculum

opencurriculum.org