PDF Stacks is described as 'With PDF Stacks, you can organize, find and browse, search, annonate and share your collection and library of PDF files, papers, research and journal articles with a single click. It saves you time: no more wondering around your computer to find a PDF file' and is an app in the Office & Productivity category. There are more than 25 alternatives to PDF Stacks for a variety of platforms, including Windows, Mac, Online / Web-based, Linux and iPhone. The best alternative is Zotero, which is both free and Open Source. Other great apps like PDF Stacks are Qiqqa (Free, Open Source), Mendeley (Freemium), JabRef (Free, Open Source) and BibSonomy (Free, Open Source).
wizdom.ai (formerly colwiz) is a free and comprehensive research management software for researchers, academics and students. With the wizdom.ai android app, you can search, add and manage publications in your wizdom.ai library on the go. Sync instantly across wizdom.
Bookends is a commercial reference management software package for Mac OS X that is used to manage bibliographies and references when writing essays and articles. Its target market is students, academics and professionals.
RefWorks - an online research management, writing and collaboration tool - is designed to help researchers easily gather, manage, store and share all types of information, as well as generate citations and bibliographies.
BibDesk is a bibliographic reference manager for Mac OS X. BibDesk is designed to help organize and use bibliographic databases in BibTeX .bib format. BibDesk integrates well with TeX for creating citations and bibliographies.
UbikReader is the new way to organize your documents. Multitask while you read, annotate, write notes and share your documents with ease. No more worrying about how to manage your large, cluttered library of documents.