The Civilization series has inspired several unofficial Civ-like games. The most notable ones are probably C-evo, Freeciv, and FreeCol. The first two resemble Civilization II, while FreeCol is a remake of the original Sid Meier's Colonization. Those three are all free to download and play, and there are some options for two or more human players to compete. There is no sign that the developers plan to stop making improvements.