HathiTrust is a large-scale collaborative repository of digital content from research libraries including content digitized via the Google Books project and Internet Archive digitization initiatives, as well as content digitized locally by libraries

The Directory of Open Access Journals (DOAJ) is a website that lists open access journals and is maintained by Infrastructure Services for Open Access (IS4OA). The project defines open access journals as scientific and scholarly journals that meet high quality standards by exercising peer review or editorial quality control and “use a funding model that does not charge readers or their institutions for access”.

arXiv (pronounced “archive”) is a repository of electronic preprints, known as e-prints, of scientific papers in the fields of mathematics, physics, astronomy, computer science, quantitative biology, statistics, and quantitative finance, which can be accessed online.