Researchers can often openly share and/or retain rights to their preprints or postprints (also called the “Author's Final Manuscript” or “Author's Accepted Manuscript”). Some researchers post these versions online in repositories (known as Green Open Access). PubMed Central, for example, allows researchers to post and search for postprints otherwise known as the “Author's Final Manuscripts”.
SHERPA/RoMEO will walk researchers through their rights to archive specific versions of research on a journal-by-journal basis.
Source: https://en.wikipedia.org/wiki/Preprint#/media/File:Preprint_postprint_published.svg
bioRxiv
bioRxiv (pronounced "bio-archive") is a free online archive and distribution service for unpublished preprints in the life sciences. It is operated by Cold Spring Harbor Laboratory, a not-for-profit research and educational institution.
medRxiv
medRxiv (pronounced "med-archive") is a free online archive and distribution server for complete, but unpublished manuscripts (preprints) in the medical, clinical, and related health sciences.
OSFPreprints
Preprints dedicated to different disciplines. Run by the Center for Open Science.
Johns Hopkins University Institutional Repository (JScholarship)
JScholarship is designed to gather, distribute, and preserve digital materials related to the Johns Hopkins research and instructional mission. Content is deposited directly by Johns Hopkins faculty and staff, and includes born-digital or digitized research and instructional materials.
More information can be found on the Sheridan Libraries Open Access Guide.