Every few years I come to a point where my Ubuntu gets rather bloated, as it is filling up with a lots of packages that I never use. So the goal is to roll the list of installed packages back to what Ubuntu ships by default and then reinstall everything I feel missing (as that's faster then trying to sort out which packages are unused). How do I do that? How can I find out if a given package is part of the default install or not?
Or simply put: Where can I find a complete list of packages that Ubuntu installs by default?