What are some alternatives?
Mendeley - Easily organize your papers, read & annotate your PDFs, collaborate in private or open groups, and securely access your research from everywhere.
Docear - Docear
Zotero - Zotero is a free, easy-to-use tool to help you collect, organize, cite, and share research.
EndNote - EndNote is the industry standard when it comes to reference management in a comprehensive format.
Paperpile - Clean and simple and reference management for the web. Sync your PDFs to Google Drive and cite your papers in Google Docs.
Papers - Papers is a research management software designed to streamline searching, aggregating and citing digital reference materials.