https://help.ubuntu.com/community/FreeNX

FreeNX is a system that allows you to access your desktop from another machine over the Internet. You can use this to login graphically to your desktop from a remote location. One example of its use would be to have a FreeNX server set up on your home computer, and graphically logging in to the home computer from your work computer, using a FreeNX client.

It’s Open Source, secure (SSH based), fast and versatile! License: GPL

FreeNX server:

sudo add-apt-repository ppa:freenx-team
sudo apt-get install python-software-properties
sudo sed -i 's/natty/lucid/g' /etc/apt/sources.list.d/freenx-team-ppa-natty.list
sudo apt-get update
sudo apt-get install freenx
wget https://bugs.launchpad.net/freenx-server/+bug/576359/+attachment/1378450/+files/nxsetup.tar.gz
tar -xvf nxsetup.tar.gz
sudo cp nxsetup /usr/lib/nx/nxsetup
sudo /usr/lib/nx/nxsetup --install
scp /var/lib/nxserver/home/.ssh/client.id_dsa.key client-user@cliet-machine:/~
sudo /etc/init.d/freenx-server start

By default, nxserver uses port 22 for communicating over SSH.
/etc/ssh/sshd_config
/etc/nxserver/node.conf
# The port number where local ‘sshd’ is listening.

SSHD_PORT=22

FreeNX client:
sudo apt-get install qtnx