Mendeley is a free tool for managing references and PDFs through either a desktop client or an account on mendeley.com. Mendeley has the following features:
- All of your research saved in one place, accessible across devices
- Read and annotate saved PDFs while on the go using Mendeley's online or offline access. You can highlight, annotate, and add sticky notes.
- Generate citations and a bibliography (compatible with MS Office, LibreOffice, & BibTeX)
- It is social, allowing for the creation of your own citation management network
Mendeley's free version is limited to 2 GB web storage (500 MB each for personal shared storage) 3 users, and 1 shared collections (1), but users have the options for purchasing premium plans for more more features.
Mendeley help links: