Cyberduck is a fairly popular file transfer client for Apple Mac and Microsoft Windows. It supports SFTP, FTP, FTPS, WebDAV, Amazon S3, and OpenStack Swift protocols.
Cyberduck was built by David V. Kocher, Yves Langisch, and iterate GmbH.
Cyberduck can be downloaded from https://cyberduck.io/.
Opening SSH tunnels from the external Internet into organizations has also become a common way to circumvent security policies and open backdoors. More information