Zotero - Free and Open-source research assistant

Zotero is a free tool for collecting, organizing, annotating, citing, and sharing research. It's available for Mac, Windows, Linux, and iOS devices. Zotero automatically detects research materials while browsing the web. Users can organize these materials into collections or tag them with keywords. The tool also generates citations and bibliographies in various formats. Zotero offers collaboration features and the ability to sync data across devices. It is open-source and developed by a nonprofit organization.

Zotero's storage pricing options are as follows:

1. Free plan: 300 MB storage.
2. $20/year ($1.67/month): 2 GB storage.
3. $60/year ($5/month): 6 GB storage.
4. $120/year ($10/month): Unlimited storage.