RefWorks is available through the University of Maryland College Park. For more information and to sign up go to RefWorks: Online Tool for Managing Citations
Cost: free while affiliated with UMD (Sign up)
Writing Plugins: Word
Browser Integration: bookmarklet; Firefox extension
Groups: Private only
Desktop Clients: None with Basic; paid desktop version
EndNote Basic (formerly EndNote Web) is the online-only version of EndNote, the popular desktop citation software. The desktop version is quite expensive, but EndNote Basic is free. EndNote Basic is good when you want a no-frills, entirely web-based citation management platform, but Zotero and Mendeley have more features.