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.
Ideanote - Ideanote is the #1 rated Idea Management solution for companies of all sizes. Collect, develop and manage more of the right ideas from customers and employees to drive your growth.
Mendeley - Easily organize your papers, read & annotate your PDFs, collaborate in private or open groups, and securely access your research from everywhere.
Monkkee - Keep a private journal securely on the Internet – to provide a convenient user experience your...
Zotero - Zotero is a free, easy-to-use tool to help you collect, organize, cite, and share research.
Idea Notebook - Idea Notebook is an app that allows you to keep track of your logs business ideas and track as well as organize them.
JabRef - Graphical Java application for managing bibtex (. bib) databases.JabRef · JabRef Help · JabRef | Blog · OpenOffice/LibreOffice .