program that can find unused packages, e.g. libraries

 deborphan finds "orphaned" packages on your system. It determines which
 packages have no other packages depending on their installation and shows
 you a list of these packages. It is most useful when finding libraries,
 but it can be used on packages in all sections.
 .
 This package also includes orphaner, a text menu frontend to deborphan.
 Please install the recommended packages dialog, gettext-base and apt when
 you want a working and fully featured orphaner.