Broad Material
Sci-Hub (the url changes to often to bother linking it)
Z-Lib (can be accessed by Tor. If you have an account, they give you a clearnet url that will only work for your account)
Library Genesis (the url changes to often to bother linking it)
Anna’s Archive: https://annas-archive.org
Open access textbooks: https://open.umn.edu/opentextbooks
Sacred Texts Archive: https://www.sacred-texts.com/index.htm
Lots of Books: https://onlinebooks.library.upenn.edu/archives.html
Internet Archive: https://archive.org/details/texts
Project Gutenberg: https://www.gutenberg.org
Roy Glashan’s Library: http://freeread.com.au
Trove: https://trove.nla.gov.au/
Hathi Trust: https://www.hathitrust.org
Antiquity
Perseus Catalogue: https://catalog.perseus.org
Internet Classics Archive: https://classics.mit.edu/index.html
Medical texts
British Medical Journal: https://www.ncbi.nlm.nih.gov/pmc/journals/3/#brmedj
Free Medical Journals: http://www.freemedicaljournals.com
Medical Journal of Australia: https://catalog.hathitrust.org/Record/000499859 and https://dayofdifference.org.au/t-medical/the-medical-journal-of-australia-archives.html and https://www.mja.com.au/journal
Connected Histories — A bunch of primary sources from England, 1500-1900: https://www.connectedhistories.org
Early English Books: https://quod.lib.umich.edu/e/eebogroup/
Western Esoterica: http://www.esotericarchives.com/index.html
Historic Australian TV: https://archive.org/details/Historic-Australian-TV-Uploads