Think of it as an iTunes for your PDFs.
Features include:

• search / download / import PDFs (and misc. metadata) from ACM, IEEE, PubMed and CiteSeer
• automatic "bibtex and PDF finder" for other URLs
• manage relations between authors, papers, organizations, sources, publishers
• organize papers into collections
• search your local library, including full metadata and text extracted from PDFs
• make notes right into your PDF, indexed by page
• automated importation of referenced and "cited by" document links
• automated resolution of "these two authors are the same" issues (for authors, organizations, publishers, sources, etc)
• "smart" playlists store searches of your local library or any of the supported import sources
• rate papers and authors on quality

Operating systems: Windows, Linux
Screen libraries: Gnome
Dependencies: Python, sqlite