Zotero is a tool for importing and managing bibliographic citations and creating bibliographies of those citations. It was created in 2006 by the Roy Rosenzweig Center for History and New Media at George Mason University, which continues to manage and develop it today.
Zotero is available for Mac, Windows, and Linux. The plug-in is for Firefox, while the Standalone is a separate application that also connects to your browser (choice of Firefox, Chrome, or Safari) and includes plug-ins to Word and OpenOffice.
Zotero's basic File Storage plan (300mb of storage) is free, but there is a charge for more storage:
(Source: Zotero File Storage)
Zotero does not charge for collaboration between users, and allows for institutional storage plans.
Citation styles are written in the XML-based Citation Style Language (CSL). Citation management tools all come preset with many of the major styles (APA, MLA, Chicago, AMA, etc.) but Zotero can also import new CSL files to format your citations in the style of whatever journal or publisher with whom you might be working. Find the style you need in one of the libraries below, download the CSL file, and then import it into Zotero by going to the Preferences menu (under the Gear icon in the plug-in), then to the Cite tab, and then Styles (see the image). You can add the style you downloaded by clicking on the + button. It will then appear in the citation style options when you export your items as a bibliography.