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.
Cost: free; no UMD-affiliated account needed
Writing Plugins: Word, Open Office
Browser Integration: bookmarklet, no extensions
Groups: Public or private
Desktop Clients: Windows, Mac, Linux
Mendeley is a citation management desktop client based primarily around the cultivation of PDFs. You can import PDFs, highlight and annotate them, get readership statistics, and even choose a folder on your computer for Mendeley to "watch" for new content. Mendeley also gives you the opportunity to search across papers cultivated by other Mendeley users. Owned by Elsevier.