You can run command-line sftp (Secure FTP) tool:
sftp USER@ssh.hcoop.net Connecting to ssh.hcoop.net... Password: sftp> help
With GUI FTP clients, SFTP connection is possible if the clients support "Secure FTP" or similar as the connection method. In Unix/Gnome, you could use for example gftp; for KDE, use the sftp KIO slave (sftp://ssh.hcoop.net: in Konqueror or Dolphin); for Microsoft Windows, WinSCP is recommended.