Debian is the Operating System I use at home since 2001 and at work from 2001 to 2004.
Official website: http://www.debian.org/
There are several front-ends:
deborphan | sudo xargs apt-get remove -y
dpkg --get-selections | grep " install$"
The aptitude command might help you to find any 3rd party software package currently installed on your Debian system.
sudo aptitude search '~i(!~ODebian)'