Zotero is an open source citation manager that is free except for the option to pay for online storage beyond 300 MB. It is compatible with Mac, Windows, and Linux, and offers plugins for Word and LibreOffice. Zotero can work completely offline, store pdfs of your research, manage and generate citations and offers cloud storage for syncing and collaboration. For an introduction to Zotero's features, watch the video below. Or jump right in by visiting zotero.org.
To get started with the Zotero Research Manager, click the link below and follow the instructions to download.
Zotero Advanced