Zotero (pronounced "zoh-TAIR-oh") is a free program that collects, manages, and cites research sources. It's easy to use, lives in your web browser where you do your work, and best of all it's free. Zotero allows you to attach PDFs, notes and images to your citations, organize them into collections for different projects, and create bibliographies.
Zotero requires that you install two different applications on each computer you use for research:
With recent updates to Zotero you can manage and add items to your library using a web browser (without downloading the Zotero desktop program). Add items from a web browser plugin, with a DOI, ISBN, or other standard number, or manually by creating a citation. The Zotero Web Library is ideal for lab or shared workstations where you may not want to take the time to set up local software.
Note that the Web Library is missing some functionality you will find in the client:
New with Zotero 6!
With the New Zotero PDF Viewer you can highlight and annotate PDFs right in your Zotero application.
PDFs open in a new Zotero viewer tab, unless you choose in your preferences to keep Adobe as your default viewer.
Read more at the Zotero support page: