Freeciv

Freeciv is a free and open-source remake of Sid Meier's Civilization, originally SGI IRIX, later expanded to all possible platforms. The goal is to be a good multiplayer version of Civ and to be true to Sid Meier’s version. The game can be configured to be very close to the original DOS Civ and to Civ II, but not to any other versions of Civilization. It is a turn-based multiplayer strategy game (but human players move simultaneously), in which each player becomes the leader of a civilization, fighting to become the greatest ruler. The game ends when there is only one nation left, when the final year has been reached, or when a player builds and launches a spaceship, which reaches Alpha Centauri first.

Freeciv is maintained and constantly improved by an international team of coders and enthusiasts with full multiplayer options and extensive multilanguage support. The game comes with different modpacks that incorporate the rules of the different Civilization games as well as the popular settings of Freeciv players. You can create your own maps with the civworld editor as well. The map editor doesn't exist in a ready-to-run release yet.