Mendeley
Organize citations and PDFs through either an online account or a downloadable desktop program. Mendeley also works like social media, enabling you reach out to other researchers. Save articles and other items to your library using the Google Chrome extension.
A lightweight version of Zotero that doesn't require any installation. Very easy to use.
A tool that helps you store and organize articles and websites. Has the ability to export in NLM format and also has a Google Chrome extension. For a tutorial on how to use Zotero, stop by the Library.