Ubuntu comes with Ubuntu Software Center to handle software installation. But sometimes, Ubuntu Software Center is too heavy for an older computer. There is another alternative to Ubuntu Software Center called Appgrid which can be used to install software but it much lighter compared to Ubuntu Software Center.
Appgrid has a simple and nice interface. You can search any software from the search page and simply press Install button to install it.
How to install Appgrid on Ubuntu 13.04 Raring Ringtail
Execute the following commands to install Appgrid on Ubuntu 13.04
sudo add-apt-repository ppa:appgrid/stable
sudo apt-get update
sudo apt-get install appgrid
Once finished, you can start using Appgrid to manage your software on Ubuntu 13.04