Ftp client is such us application that help people to perform upload and download file trough ftp protocol (port 21). FTP is built on a client-server architecture and utilizes separate control and data connections between the client and server. Using ftp is give own advantages, since it's a technology would able to make the management of website much easier as it provides with a way to upload and download new or updates files to a web space in a few seconds without need anything else apart from the FTP password for the account which you wish to use to upload files from your local computer.  

How FTP Works ?
FTP works in the way that a direct connection is established between your local computer and web/ftp server via the internet using the FTP protocol. The connection is normally made on standard port for FTP that is Port 21. You can then make use of FTP to upload and download files from a web space, and in the case  while using an advanced FTP client we can also be able to carry out advanced tasks such as the setting of permissions. The connection is two-way to allow you the best flexiblity in manage your web space (http://blog.eukhost.com/webhosting/using-the-ftp-protocol/).

For ubuntu user which usually work as programer/other that familliar with upload or download from online media i think must be familiar with some FTP Client that works on ubuntu, and for the others here they are list  of Ftp Client that work well on ubuntu and other common linux.

GFTP is Opensource application Graphical FTP Client that is used on Mac OS X, UNIX, EPLF, Novell, VMS, MVS and NT. There is support for the FTP, FTPS  (control connection only), HTTP, HTTPS, SFTP and FSP protocols, as well as FTP and HTTP proxy server support and FXP file transfers (transferring files between 2 remote servers via FTP)

  • Download: Links  gftp.seul.org 
  • Command line how to Install GFTP in Ubuntu via APT  is sudo apt-get install gftp

FileZilla is FTP application that  support of Client Server that has the GNU license, and supports SSL / TLS (FTPS), SSH File Transfer Protocol (SFTP), can be used on Windows, Linux, * BSD, Mac OS X, IPv6, HTTP/1.1, SOCKS5. FieZilla Allows a user to create a list of FTP sites along with their connection data, such as the port number to use, the protocol to use, and whether to use anonymous or normal logon.
Kasablanca is Graphical FTP applications are written using C + + language using the libraries from KDE. Has an features: encryption via AUTH TLS, fxp (direct server to server transfers), bookmarking system.
  • Download Links : kasablanca.berlios.de 
  • Command line how to Install Kasablanca on Ubuntu VIA APT is  sudo apt-get install Kasablanca
KFTPgrabber is Graphical FTP client application that has the features: TLS / SSL, X509 certificates, One-time password (OTP), traffic graph. KFTPGrabber is a free and fast FTP client that can be easily integrated in KDE. 
GNOME Commander
GNOME Commander is a 'two pane' graphical file manager for GNOME. It is built using the GTK+ toolkit and GnomeVFS. GNOME Commander aims to fulfil the demands of more advanced users who like to focus on file management, their work through special applications and running smart commands (wikipedia). 
Sitecopy is Graphical FTP Client that can be used to assist the webmaster in maintaining the website, upload files, and supports WebDAV. SuSE Linux, Fedora / RHEL, Debian GNU / Linux, Ubuntu, NetBSD, Mac OS X (Fink), Slackware.
  • Command how to Install SiteCopy on Ubuntu VIA APT is  sudo apt-get install sitecopy