Is there any GUI application for command rsync?

Yes, there is available Grsync GUI App as front end of rsync tool.

Grsync is a rsync GUI (Graphical User Interface)

It is available on Universe repository for Ubuntu 14.04 and can be installed by following command:

To Enable Ubuntu repository run command (or make sure that enabled from Software & Updates):

sudo add-apt-repository "deb http://archive.ubuntu.com/ubuntu $(lsb_release -sc) main universe"

Install Grsync By following command:

sudo apt-get update
sudo apt-get install grsync

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Here is Screen-Shot of Grsync GUI Application with some steps shown below:

Source & Destination can be selected same as from rsync.

Also you can save different Session for future or often use.

I think that the most powerful application with a GUI for synchronizing is Unison. You can install it via

sudo apt-get install unison-gtk 

and it will allow you to sync directory locally, with mounted drives, and on the network via ssh connections. It detects conflicts and in that case it will ask you what to do.

It is quite easy to get started but can become very powerful if you learn how to edit the configuration files by hand; the documentation is really good. There is a command-line interface which is quite handy for scripting.