Mendeley - Easily organize your papers, read & annotate your PDFs, collaborate in private or open groups, and securely access your research from everywhere.
ProCite - ProCite is a tool for creating citations according to the standard defined by the users.
CiteDrive - CiteDrive is a cloud-first, collaborative, BibTeX-native reference manager created by and for Overleaf, LaTeX, and R Markdown users.
Pybliographer - Pybliographer is a tool that helps you manage your bibliographic databases in a user-friendly way.
Paperpile - Clean and simple and reference management for the web. Sync your PDFs to Google Drive and cite your papers in Google Docs.
I Librarian - I Librarian is an online tool that comes with a great way to handle and manage your PDF paper and office documents.