Mendeley
Mendeley is a popular, free citation manager and reference organizer that helps researchers collect, store, cite, and share academic sources (PDFs, web pages) across devices, featuring a cloud library, Web Importer for browsers, and Mendeley Cite add-in for Microsoft Word to insert citations and generate bibliographies in various styles. Owned by Elsevier, it syncs across web, desktop, and mobile, allowing annotation, collaboration, and easy reference management for writing papers.