Endnote is an application that imports citations from your searches in web databases and helps you organize your references. It works with Microsoft Word helping you create in-text citations, footnotes, and bibliographies.
Mendeley allows you to share references with others or to maintain a private library. Mendeley collections can be exported to Endnote, CiteULike, or Zotero libraries. Mendeley works with Word 2008 and OpenOffice to insert citations into your documents. It enables you to extract citation information from downloaded pdfs.
Zotero is a plug-in from Mozilla that you use with the Firefox browser. Simply download the plug-in, activate the Zotero application by clicking on the Zotero icon in your browser. You can now capture citations into a library held on your hard drive or on a flash drive.
Zotero works with Word and OpenOffice after you have downloaded the plug-ins.