Docear is a unique solution to academic-literature management: it helps you in organizing, creating, and discovering academic literature.
Among other things, Docear offers:
A single-section user-interface that allows the most comprehensive organization of your literature. With Docear, you can sort documents into categories; you can sort annotations (comments, bookmarks, and highlighted text from PDFs) into categories; you can sort annotations within PDFs; and you can view multiple annotations of multiple documents, in multiple categories -- at once.
A 'literature suite concept' that combines several tools in a single application (PDF management, reference management, mind mapping, ...). This allows you to draft your own papers, assignments, thesis, etc., directly in Docear and to copy annotations and references from your collection directly into your draft.
A 'recommender' system that helps you discover new literature: Docear recommends papers which are free, in full-text, instantly ready to download, and tailored to your information needs.
And did we mention that Docear is free, open source, available for Windows, Linux, and Mac OS X, not evil (open data formats such as BibTeX and XML, no registration required, no lock-in), and offers PDF metadata retrieval, free online-backup of your mind-maps, free support (German and English), a monitoring function for new files (PDFs, images, etc.), a free MS-Word add-on, ...?