There might be a new add-on for Civilization 5 coming according to files discovered on the Steam App Store.
The potential new content, called "One World," was uncovered by Joystiq. On the Steam App Store, there is an executable file for the expansion on PC. The previous add-on, "Gods and Kings," was made available for both PC and Mac. No other details about what "One World" might be were listed, but that hasn't stopped speculation from running rampant.
Rumors are all over the place as to what to expect, including a belief the expansion will somehow tie into the last season of the Survivor television series. Until Firaxis offers up a bit more concrete information, we'll just have to hope Jeff Probst isn't making an appearance.