Unknown Horizons is a RTS game focused on building your city and its economy, commerce.
Install Unknown Horizon
Add following source to your /etc/apt/sources.list file.
deb http://deb.unknown-horizons.org/ release main
Install GPG keys of the repo to confirm package authenticity.
wget http://deb.unknown-horizons.org/key && sudo apt-key add key
Now update your apt cache to fetch info about new packages and install Unknwn Horizons game.
sudo apt-get update && sudo apt-get -y install unknown-horizons