Mendeley
https://www.mendeley.com/
Mendeley is a free reference manager and academic social network that can help you organize your research, collaborate with others online, and discover the latest research: automatically generate bibliographies; collaborate easily with other researchers online; easily import papers from other research software; find relevant papers based on what you’re reading; access your papers from anywhere online.
Help Guides
Zotero
https://www.zotero.org/
This free easy-to-use tool to help you collect, organize, cite, and share research. Available for Mac, Windows, and Linux. More information…
Quick Start Guide/