Download of iPapers 2.2 for Mac was on the developer's website when we last checked. We cannot confirm if there is a free download of this app available. This free software for Mac OS X was originally developed by Toshihiro Aoyama. IPapers for Mac is categorized as System Tools. Please check the Mac app with an antivirus before launch as it is downloaded from the developer's website, and we cannot ensure that it is safe.
From the developer:
iPapers is an application that manages many PDF files of articles, whose information can be obtained by PubMed. If you have articles as PDF files whose filenames are PMID.pdf (e.g. 10867176.pdf), you can import the articles into iPapers by drag and drop operation. PMID is the unique ID provided by PubMed. iPapers automatically searches and imports the information of the imported articles from PubMed DB, e.g.
You may want to check out more software for Mac, such as pdf-FieldMerge, which might be similar to iPapers.