Zotero is free, open-source reference management software with a desktop version and an online version. The Zotero Connector browser extension makes it easy to collect references while you're searching. Zotero's cloud-based storage is limited, but you can pay to upgrade storage. You can use Zotero to cite while you write using MS Word, Google Docs, or LibreOffice. You can also annotate PDFs within Zotero. More details are available in the Choosing Reference Management Software table.