Install the SpreedX repository for Ubuntu:

  ~$ sudo add-apt-repository http://dl.spreed.com/linux/spreedx/deb
  ~$ wget -qO- http://dl.spreed.com/struktur-debian-package-sign-01-public.key | sudo apt-key add -
  ~$ sudo apt-get update
  ~$ sudo apt-get install spreedx

Start Spreed Screen Sharing using Unity Dash (just type Spreed) or run "spreedX" in a terminal.