It involves staking claims to virtual territory using their phones GPS, and in-game gold is awarded to players. It brings "gaming out of the home".
"The faction with the greatest number of flags in any given territory at any given time will “conquer” that land – changing it in colour and following to either the Rebels or the Royals," reads the official press release.
"Players will be rewarded for their allegiance and efforts in capturing territory with in-game “Gold” which may be transferred into the full game of “Fable III” on Xbox 360* when it launches across Europe on 29th October."
It would appear that Kingmaker is Fable III's very own Pub Games equivalent that released for Fable II. Earnt in-game gold can be spent on anything in the full Fable III game from clothing, weapons to homes and whatever else the RPG has to offer.
“To be able to earn gold you can use in your Fable III game, and to check-in and claim land for your side is brilliant for both Fable III and Xbox 360. We all love the innovation and feeling of being connected that Kingmaker brings to gamers,” said Peter Molyneux.
This mobile title will be available in the UK, France, Germany, Spain, Italy, Netherlands and Sweden. “Fable III: Kingmaker brings gaming out of the home and turns your town or city into the setting for an epic online battle," said Microsoft's Chris Lewis.
"We are always challenging ourselves to find new, exciting ways to deliver second-to-none gaming experiences and we can’t wait to see Fable fans take to the streets across Europe with Fable III: Kingmaker." Fable III Kingmaker releases October 4th, while Fable III releases on Xbox 360 October 29th in Europe, and on PC at a later date.