Although there is a free online version of Endnote, this guide mostly refers to the desktop version (EndNote 21) that must be purchased. UofA students and faculty can get a discounted price at ualberta.onthehub.com.
Best features: Can store 1 million references and PDFs; deduplicates large numbers of references; many reference types (helpful for accurate citation); highly customizable; ability to work offline.
Drawbacks: Price (~$140); license tied to one device; steeper learning curve than other options; no Google Docs integration (only MS Word and LibreOffice).
Information on configuring EndNote to access library resources as well as tip sheets on importing records into EndNote from our major database platforms: