"When you love Dropbox like we do, you start syncing more and more stuff. The more stuff you sync, the harder it is to organize. Here's a simple way to sort quickly and stay organized across multiple computers, Windows, Mac, or Linux. We're going to deal with two things here: organization and synchronization."
"There's lots of citation management tools out there, but one of the primary reasons I recommend the free and open-source Zotero tool from CHNM is its automatic syncing service, and ability to share sources - with PDF attachments - in a group library, such as a class or research team. Here's a quick tutorial, and see additional details on the Zotero support page."