I know how to check if a package is installed and if its available for install but I cannot find any list of packages that are installed with a release from Ubuntu.

Sometimes I am trying to answer something and I cannot remember if the tool I will refer was installed by default of if I installed in a later point and cant remember. What if its something I have and a user using another desktop environment does not?

I know I can recommend to install the package prior to asking him to use it but I would like to know if its installed by default or not.

Is there such list? Where can I find it?