https://www.raspberrypi.org/forums/viewtopic.php?p=890408#p890408

This next part focuses on installing a GUI on top of Raspbian Lite. In order to have a GUI, we need these 4 things:
1. Display Server
2. Desktop Environment
3. Window Manager
4. Login Manager

1. Xorg Display Server
2. Raspberry Pi Desktop (RPD) or Lightweight X11 Desktop Environment (LXDE) or XFCE Desktop Environment (XFCE) or MATE Desktop Environment (MATE)
3. Openbox Window Manager (RPD/LXDE) or XFWM Window Manager (XFCE) or Marco Window Manager (MATE)
4. LightDM Login Manager

sudo apt-get install --no-install-recommends xserver-xorg xserver-xorg-legacy
#When not using login manager, install xinit:
sudo apt-get install --no-install-recommends xinit

Stripped down version of RPD (Raspberry Pi Desktop):
sudo apt-get install --no-install-recommends raspberrypi-ui-mods lxsession

optional:
pi-greeter : The Raspberry Pi LightDM login theme
rpd-icons : The Raspberry Pi Desktop icon theme
gtk2-engines-clearlookspix : GTK Theme Engine (used to render Raspberry Pi LightDM login/desktop theme properly)

Openbox WM is installed by default when using RPD.

with xinit, system starts in command line. When required, use startx to start GUI

Single application setup:

#Disable avahi
#The Pi is going to use simple uni-cast DNS - multi-cast DNS support is not required.
sudo systemctl disable avahi-daemon
sudo systemctl stop avahi-daemon

#Disable TriggerHappy
#The Pi isn't being used with button. Disable the TriggerHappy daemon (not that it is a init.d service)
sudo systemctl disable triggerhappy
sudo systemctl stop triggerhappy 

#When not using nfs remove:
sudo apt-get remove –purge nfs-common

sudo apt-get install --no-install-recommends xserver-xorg
# sudo apt-get install xserver-xorg-input-evdev
sudo apt-get install --no-install-recommends xinit
sudo apt-get install openbox lxterminal
#sudo apt-get install lightdm
echo "exec openbox-session" | tee ~/.xinitrc

sudo apt-get install linphone

sudo dpkg-reconfigure xserver-xorg-legacy

set anybody

sudo vi /etc/X11/Xwrapper.config

allowed_users=anybody
needs_root_rights=yes

sudo usermod -a -G audio,tty,video,users pi

sudo vi /etc/xdg/openbox/autostart

/usr/bin/linphone & #set the program to start

#disable right-mousebutton in openbox: 
sudo vi /etc/xdg/openbox/rc.xml

#comment out these lines using <!-- and -->

<!-- 
#    <mousebind button="Right" action="Press">
#      <action name="Focus"/>
#      <action name="Raise"/>
#      <action name="ShowMenu"><menu>client-menu</menu></action>
#    </mousebind>
-->

sudo vi /etc/systemd/system/kiosk.service

[Unit]
Description=Kiosk

[Service]
Type=oneshot
ExecStart=/usr/bin/sudo -u user /usr/bin/startx --

[Install]
WantedBy=multi-user.target

sudo systemctl enable kiosk
sudo systemctl start kiosk