Aigaion Reference Management System - Aigaion is a bibliography management system that seems to be the perfect tool for managing your bibliography and references.

Zotero - Zotero is a free, easy-to-use tool to help you collect, organize, cite, and share research.

Pybliographer - Pybliographer is a tool that helps you manage your bibliographic databases in a user-friendly way.

Mendeley - Easily organize your papers, read & annotate your PDFs, collaborate in private or open groups, and securely access your research from everywhere.

I Librarian - I Librarian is an online tool that comes with a great way to handle and manage your PDF paper and office documents.

Paperpile - Clean and simple and reference management for the web. Sync your PDFs to Google Drive and cite your papers in Google Docs.