Login/window manager information
dpkg -l | grep -i kde > kde.txt
dpkg -l | grep -i plasma > plasma.txt
dpkg -l | grep -i gnome > gnome.txt
dpkg -l | grep -i xfce > xfce.txt
dpkg -l | grep -i metacity > metacity.txt
dpkg -l | grep -i unity > unity.txt
dpkg -l | grep -i gdm > gdm.txt
dpkg -l | grep -i sddm > sddm.txt
dpkg -l | grep -i lightdm > lightdm.txt
dpkg -l | grep -i kodi > lightdm.txt
dpkg -l | grep -i carousel > lightdm.txt
dpkg -l | grep -i compiz > compiz.txt

Unity information
sudo apt-get purge unity-* libunity-*

e.g. gnome uninstall
sudo apt-get purge gnome-* libgnome* gconf-service gconf-service-backend gconf2-common libgoa-1.0-0b libgoa-1.0-common ubuntu-sounds unity-control-center account-plugin-facebook  account-plugin-flickr account-plugin-google account-plugin-windows-live baobab empathy-common gcr gparted language-pack-gnome-* libp11-kit-gnome-keyring:amd64 libxml2 libxml2-dev nautilus signon-keyring-extension brasero epiphany-browser-data gedit-common libpam-gnome-keyring libreoffice-gnome libxml2 remmina screen-resolution-extra usb-creator-gtk vino

e.g. kde uninstall
sudo apt-get purge libplasma*
sudo apt-get purge plasma-*
sudo apt-get purge libkresources4
sudo apt-get purge libkwinglutils6
sudo apt-get purge apport-kde kdegraphics-strigi-analyzer kdepimlibs-kio-plugins kdesudo libakonadi-kde4 libkwineffects6 libkwinxrenderutils6 libpam-kwallet4 libphonon4 libphonon4qt5-4 libreoffice-kde phonon libpimcommon5 liblockdev1
sudo apt-get purge xfwm4 compiz-core compiz-gnome libmetacity-* metacity-common libdecoration0

Final cleanup
sudo apt-get autoremove