Cyberduck is a storage browser available from https://cyberduck.io/ that supports accessing files over SFTP using Public Key Authentication. It is available for OSX and Windows.
There is no permanent solution for getting the SSH_AUTH_SOCK environment variable into the application like you can with other documented OSX based clients such as SequelPro. This means that you need to launch Cyberduck from a Terminal shell.
As part of the installation of Desktop Agent some entries are made to your ~/.bash_profile to point supporting clients to the socket used for communication with the agent. Launching Cyberduck from Finder does not pick these up. If you open a terminal and open the command it will use the correct settings:
open /Applications/Cyberduck.app/The Windows version of Cyberduck in theory supports PuTTY’s Pageant, for which we have inbuilt support for. However at this time we have been unable to prove this to be the case and have not been able to get Cyberduck on Windows to communicate with our own Pageant interface.