Graphical front-end to apt, the package management system in Ubuntu.
The Synaptic Package Manager is a GUI program that is designed to graphically give a user access to advanced package management, with the ability to modify almost any aspect of the apt repository information, as well as to be able to view a complete list of all known packages. Synaptic has the ability to show you specifics about installed packages, including what its dependencies are (and it will install a package's dependencies if you tell the system to install a package), what files are included in the package, and also gives you the ability to remove/purge/update/upgrade packages as the user deems necessary.