Zotero is a free online referencing system that you can use on the web and on your desktop. You can create your own fully-searchable reference library, cite as you write and read and annotate your PDFs. It also functions as an academic social network; you can create your own researcher profile.
Unlike EndNote, Zotero is not supported by the university. This guide will give you some initial help, and refer you to Zotero help resources online.
How to install Zotero (Georgia State University Library)