This question is in reference to another question that has not been answered. When I upgraded Ubuntu, all my PPAs were removed (which I'm ok with). Is there a way to list all the packages that no longer have a repository associated with them?
APT refers to these packages as "obsolete".
Evidently there is no direct way to list these, but you could do:
aptitude search '~o'
apt-show-versions | grep 'No available version'
If you want a GUI tool you can do this with Synaptic by using the built-in "local or obsolete" filter.