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.

Zotero - Zotero is a free, easy-to-use tool to help you collect, organize, cite, and share research.

MindMeister - Create, share and collaboratively work on mind maps with MindMeister, the leading online mind mapping software. Includes apps for iPhone, iPad and Android.

Google Scholar - Google Scholar is a freely accessible web search engine that indexes the full text of scholarly...

Coggle - Coggle is a simple, beautiful, powerful way of structuring information.