ChemSpider is a free chemical structure database providing fast text and structure search access to over 32 million structures from hundreds of data sources.

The OSF Preprints search combines records from various preprint repositories, including arXiv, bioRxiv, Cogprints, PeerJ, PsyArXiv, RePEc and SocArXiv.

SocArXiv, open archive of the social sciences, provides a free, non-profit, open access platform for social scientists to upload working papers, preprints, and published papers, with the option to link data and code. SocArXiv is dedicated to opening up social science, to reach more people more effectively, to improve research, and build the future of scholarly communication.