arXiv - an e-print archive for the fields of physics, mathematics, computer science, quantitative biology, quantitative finance, statistics, electrical engineering and systems science, and economics.
bioRxiv - a free online archive and distribution service for unpublished preprints in the life sciences operated by Cold Spring Harbor Laboratory.
ChemRxiv - a free submission, distribution, and archival service of the American Chemical Society for unpublished preprints in chemistry and related areas.
Figshare - allows researchers to make different types of research outputs, including presentations and datasets, available.
Humanities Commons - a trusted, nonprofit network where humanities scholars can create a professional profile, discuss common interests, develop new publications, and share their work.
OAPEN - freely accessible academic books, mainly in the humanities and social sciences.
Optica Open - a free, open, moderated preprint server for unpublished research in optics and photonics. Submissions are screened prior to acceptance, and those not meeting Optica Open's criteria are declined.
PeerJ Preprints - published screened, but not peer-reviewed, preprints in biological sciences, environmental sciences, medical sciences, health sciences, computer sciences, and chemistry.
PubMed Central - (PMC) is a free full-text archive of biomedical and life sciences journal literature at the U.S. National Institutes of Health's National Library of Medicine (NIH/NLM).
SSRN - a repository of open access pre-prints in social sciences, including economics, law, corporate governance, and humanities.
TechRxiv - an open, moderated preprint server for unpublished research in electrical engineering, computer science and related technology.
