What is Zotero?
"Zotero [zoh-TAIR-oh] is a free, easy-to-use tool to help you collect, organize, cite, and share your research sources." – www.zotero.org
Zotero has two main forms: an add-on for Mozilla Firefox, and a standalone application. Your saved citations can be archived and shared between copies of the software with an online (free) account on zotero.org.