Qiqqa is by far the strongest solution for research and managing pdf's. Zotero, named as a comparison is weak as it does not allow pdf;s to be loaded into its interface - you need to use a pdf reader, which defeats its whole purpose. With Qiqqa documents in a library can be searched together. It has excellent maps of your libraries. It is not prefect, having a few glitches, but still is the only one of its kind.
NationBuilder - The world's first platform for leaders, handcrafted from scratch to help you grow your community and lead them to action.
Mendeley - Easily organize your papers, read & annotate your PDFs, collaborate in private or open groups, and securely access your research from everywhere.
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Zotero - Zotero is a free, easy-to-use tool to help you collect, organize, cite, and share research.
Intranet Quorum - Customer focus, innovation and purpose are built into everything we do. When millions of people are counting on you. You can count on us. Lockheed Martin. Your Mission is Ours.
JabRef - Graphical Java application for managing bibtex (. bib) databases.JabRef · JabRef Help · JabRef | Blog · OpenOffice/LibreOffice .