UPDATE November 2015
The new Remastersys is Pinguy Builder and there is also an app called Systemback which I prefer personally. Here is how you can install it:
sudo add-apt-repository ppa:nemh/systemback
sudo apt-get update
sudo apt-get install systemback
UPDATE 05.01.2015
The link I provide in this and other instructions in step 2 does not work anymore. However, I had downloaded the Remastersys files before the website shut down and they can be installed perfectly through Ubuntu Software Center.
!! I am not sure if the files are available in Ubuntu Software Center, but if you have them on your computer, they can be installed through it.
This set of instructions helped me install and run successfully remastersys on Ubuntu 14.04.1 32-bit
Press Ctrl+Alt+T and run
sudo apt-get install plymouth-x11
Go to this link and download remastersys version for 32bit or 64bit system
http://www.remastersys.com/ubuntu/pool/main/r/remastersys-gui/
Open Software&Updates (search in Dash or in the System's parametres)
In Software&Updates, go to Other tab and press Add...
Copy/paste this
deb http://www.remastersys.com/ubuntu precise main
and press OK
Now look for two lines with "www.remastersys.com/" in the list you can find on the Other tab and make sure you check both boxes. Enter a password if you are asked to.
Press Ctrl+Alt+T and run
sudo -i
apt-get install remastersys-gui
To open remastersys-gui, you always need root priveleges. So do it in the terminal (Ctrl+Alt+T)
sudo -i
remastersys-gui