Zotero is a free, open-source reference manager run by the non-profit, Roy Rosenzweig Center for History and New Media. You can store all types of files in your Zotero account along with their references.
- Requires desktop installation on a PC or Mac
- Comes with 300MB of free storage with options to upgrade storage to 2 GB, 6 GB or unlimited - see Storage Pricing
- Can organize and store references in parent and child folders
- Creates bibliographies in over 100,000 citation styles
- Consistently captures references and documents using the Zotero Connector for Firefox, Chrome, Safari, or Microsoft Edge
- Provides plug-ins for Microsoft Word and OpenOffice to allow insertion of in-text citations and dynamic bibliographies
- Export files are compatible with BibTeX, EndNote, Mendeley, and RefWorks
Sign up for your free Zotero account at https://www.zotero.org/. You can purchase additional storage through annual fees - see Upgrade Storage at the top right. A comparison of reference managers is available in Wikipedia.