freeciv (version 2.5.0)
A clone of the well known game Civilization by Microprose. Every player is the leader of an imaginary nation. The aim of the game can be to create a prospering civilization with commerce and knowledge exchange or (more often) the extinction of all other civilizations. To start a new game, first start the server 'freeciv-server,' then start the client 'freeciv-gtk2'. Have fun!