Mendeley is a research and citation management tool that helps you collect and organize citations and sources, as well as produce bibliographies in a variety of citation styles. Mendeley lets you work both on your own computer and on the cloud, capturing citations, uploading and annotating PDFs, and sharing your documents with other researchers. The basic version of Mendeley is free; this includes limited online storage and collaboration capabilities. Users can upgrade to the Premium version for more storage and/or to share their libraries with more people.
A mobile version of Mendeley is also available for iOS devices (iPhone and iPad).
Tutorials and guides for the latest version of Mendeley: