arXiv
arxiv.org
Read tomorrow's physics papers before they're published
Deep Archives
The open half of the library everyone else pays for
about.jstor.org
Rabbit hole · Best on desktop
Free, no sign-up · online since 1995
JSTOR's open collections take in thousands of open-access journals and ebooks, early journal content published more than ninety-five years ago, research reports from well over a hundred think tanks, and close to a million images from museums and archives. A free personal account adds another hundred articles every thirty days.
The early journal content is the sleeper: century-old papers in which scientists argue with each other at length and often in magnificently bad-tempered prose.
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Picked for a shared category and overlapping vibe, not for popularity.
arxiv.org
Read tomorrow's physics papers before they're published
biodiversitylibrary.org
Every natural history book, scanned by the world's museums
davidrumsey.com
A hundred thousand old maps, zoomable to the street
indianculture.gov.in
India's national collections, digitised into one place
archive.org
Millions of scanned books, magazines and old manuals
openlibrary.org
One catalogue page for every book ever published