I remember that OSX colleagues used to be quite enthusiastic about Papers. As a Linux and sometimes Windows user, I used to use Mendeley quite intensively, until I rediscovered Zotero, which is open source, and for my use case much better than the competition.<p>Zotero is cross-platform; it enables me to sync my papers in whichever way I choose and its bibliographic data extraction and PDF downloading work much better that that of Mendeley, because it does this from your computer, not via their servers, meaning you have access to all the fulltexts that your institution has access to.<p>I've used Zotero to write a bunch of papers, book chapters and part of a book. It's very solid.