If you struggle to keep tabs on PDF documents scattered all over your hard disk, then the gPapers tool can come in rather handy. Described as "iTunes for PDFs", this Gnome-based application sports a few clever features that can help you to manage PDF documents with consummate ease. Here is what you can do with gPapers:

• Search, download, and import PDFs from ACM, IEEE, PubMed and CiteSeer.
• Manage relations between authors, papers, organizations, sources, publishers.
• Organize papers into collections.
• Search your local library, including full metadata and text extracted from PDFs.
• Annotate PDF documents.
• Save searches as "smart playlists".
• Rate papers and authors on quality.

gPapers is available as a source distribution only, so installing it requires some manual work. Fortunately, you can find a detailed description of the installation on the project's Google Code page.