What are some alternatives?
Mendeley - Easily organize your papers, read & annotate your PDFs, collaborate in private or open groups, and securely access your research from everywhere.
XMind - XMind is a brainstorming and mind mapping application.
Qiqqa - Qiqqa is a free research and reference management software. It can be used in many organizational projects from the academic to the personal to the business endeavor. Read more about Qiqqa.
MindMeister - Create, share and collaboratively work on mind maps with MindMeister, the leading online mind mapping software. Includes apps for iPhone, iPad and Android.
JabRef - Graphical Java application for managing bibtex (. bib) databases.JabRef · JabRef Help · JabRef | Blog · OpenOffice/LibreOffice .
TheBrain - TheBrain: The Ultimate Digital Memory