Unciv

Unciv is an open-source 4X game that unofficially implements the (unpatented) rulesets of vanilla Civilization V and its Gods and Kings expansion with very few disclosed "Intentional departures from Civ V". Unciv is presented in fully 2D pixelated graphics, sharply contrasting the game it's based on.

The game has cross-platform multiplayer on self-hosted servers. The server software for Unciv is distributed separately from the game's executable as a platform-agnostic Java Archive file.