apt - Advanced Package Tool

apt

Remove dependencies that are not needed any more

sudo apt autoremove

apt-mark

apt-mark showmanual
apt-mark showauto

remove a package

sudo apt remove <PACKAGE_NAME>

remove package and it's config

sudo apt purge <PACKAGE_NAME>

determine what program that is needed for a file

apt-file search

Example: apt-file search /etc/ssh/sshd.conf

list files related to a specific program

apt-file list

Example: apt-file list tree