Open Access

OA archives or repositories do not perform peer review, but simply make their contents freely available to the world. They may contain unrefereed preprints, refereed postprints, or both. Archives may belong to institutions or disciplines, such as physics and economics. Authors may archive their preprints without anyone else's permission, and a majority of journals already permit authors to archive their postprints. (see Authors' Rights) 

• Dimensions  Includes articles published in scholarly journals, books and book chapters, and preprints and conference proceedings. Publications include linked data sets, funding, publications, patents, clinical trials, and policy documents. You can also view associated categories, funders, institutions, and researcher profiles.
• Open Library of Humanities  Note: OLH has recently announced the development of an open source translation tool that will allow users to write and view translations of any web pages.
• PLoS ONE: Public Library of Science An international, peer-reviewed, open-access online publication for all scientific disciplines. Associated scientific content available at this site include PLoS Biology, PLoS Medicine, PLoS Genetics, PLoS Neglected Tropical Diseases, PLoS Pathogens, and PLoS Computational Biology. 
• Scientific Information System Redalyc.   Network of Scientific Journals from Latin America and the Caribbean, Spain and Portugal - includes citations for journal articles, some full-text articles and socio-economic indicator sources. (Note: Site is in Spanish)
• Humanities CORE In September 2016, the Modern Language Association (MLA) and Columbia University Libraries announced the award of a grant from the National Endowment for the Humanities to begin development of the Humanities Commons Open Repository Exchange (Humanities Core). 
• Share  A project of the Center for Open Science and the Association of Research Libraries. Indexes the metadata of multiple preprint servers and serve as a central place to find information on journal article preprints.
• In August 2016, the American Chemical Society announced the development of ChemRxiv a "chemistry preprint server for the global chemistry community, proposed as a collaborative undertaking that will facilitate the open dissemination of important scientific findings." 
• PubMed  more than four million articles from the NIH and six other Federal agencies in a standardized, machine-readable XML format.
• SocArXiv A server for social science research that provides access to preprints of research papers to the scholarly community at an early stage, permitting the author to incorporate community comments into the final version of the paper before its publication in a journal. Authors and papers are ranked by their number of downloads, which is an informal indicator of impact on prepress and open access sites.   While access to the published paper may be restricted, access to the original working paper remains open through SSRN.  Requires free registration.
• Social Science Open Access Repository (SSOAR) is a growing collection of full-text social-science documents which you can access freely. To search for documents, you can use either the simple or advanced search option or the browse and search function.
• American Chemical Society ACS Central Science Highly selective and multidisciplinary. No fees to libraries. No fees to authors. 
• Center for Research Libraries  Beginning in January 2017, all digital materials hosted on the web by the CRL, that derive from source materials in the public domain or for which CRL has secured the requisite rights and permissions, will be available without restriction.