Which packages are installed (on Ubuntu)

If you’re using a Debian based Linux Desktop such as Ubuntu, Linux Mint - or Debian itself naturally - you can easily create a simple text file of all packages installed on the machine. I have a habit of removing a lot of the “extras” (junk) which comes with the basic install - not religiously, but just to keep it reasonably tidy and not have too much stuff eating up the harddisk, requiring updates (without providing any value).