Searching for open source literature management software
I have been in your shoes before and am currently looking for some form of pdf organization.  

Here are a few alternatives : http://alternativeto.net/software/mendeley/

What I use, is dropbox.  I even dropped Mendeley because it didn't sync well with android for annotations.  I can favorite papers I need to have on my phone/tablet at all times and always have access to them.  My fellow cohort feels the same way about the lack of pdf organization as we generally just print out what we need.  I've been searching for years and the only thing I can come up with is paper.

Sorry this is isn't more useful, but from my experience, paper is really the way to go.