Dropbox currently supports the use of a FIDO Security Key when signing in to dropbox.com using the Chrome or Firefox web browsers.
Dropbox
More Commercial Deployments

Shinhan Bank
Shinhan Bank in Korea uses FIDO-based fingerprint authentication to access its Sunny Bank mobile application.…

PLUSCARD
PLUSCARD, a full-service processor for 140 financial institutions across Germany, worked with Entersekt and its…