When is Civilization not Civilization? When it’s Unciv, a free to play, open-source reimagining of Sid Meier’s Civilization V that’s being developed by volunteers on GitHub. After nearly three years in development and releases on Android, Linux, and through itch.io, Unciv’s now moving its units onto Steam. You'll be able to play multiplayer Unciv, but that involves using Dropbox for syncing, which isn’t free to use.
Describing Unciv as “an open-source reimplementation of the most famous civilization-building game ever”, dev Yair Morgenstern is working with volunteers using the cross-platform framework libGDX. Morgenstern says that Unciv is good if you’re looking to play something that’s a “small, fast, moddable, FOSS [free open source software] and in-depth 4X that can still run on a potato”. If you’re more interested in graphical excellence, animations, and a soundtrack then Morgenstern instead suggests sticking with Civilization V.
Unciv should eventually have every feature of the original Civ 5, Morgenstern hopes. As for potential legal issues with the project, the dev doesn’t believe there should be any and points to the example of Flappy Bird clones. Unciv doesn’t use the Civilization name, impersonate the game, or take assets from the original Civ 5. The Unciv team are still looking for more people to help with the project, including programmers, translators and modders. You can read more about Unciv and its development on the GitHub page here.