Zotero will run on any operating system. The plug-in or add-on requires Mozilla Firefox 3.0 or greater and installation only takes a few seconds. Zotero Standalone can work with any browser, although it does not offer some of the features the plug-in version allows.
If you have any problems, check the Zotero installation page. Zotero offers word processing plugins for Word and OpenOffice. The plugin adds a Zotero toolbar to your word processor that allows you to add citations to your document while you write.
Organize research, collaborate, and discover new knowledge [Mendeley]
Mendeley Desktop organizes your research paper collection and citations. It automatically extracts references from documents, generates bibliographies, and is freely available on Windows, Mac OS X and Linux.
Mendeley Web lets you access your research paper library from anywhere, share documents in closed groups, and collaborate on research projects online. It connects you to like-minded academics and puts the latest research trend statistics at your fingertips.
Visit their website for more information and tutorials on how to use the citation management service.