Warhammer Age of Sigmar: Storm Ground was announced during Gamescom's Opening Night Live, finally making the number of Warhammer games greater than Earth's entire population. It's their planet now.
Storm Ground is being touted as the first strategy game based on Age of Sigmar, forgetting about Warhammer Age of Sigmar: Champions and Warhammer Underworlds: Online, two strategy games based on Age of Sigmar. Technically they're based on Age of Sigmar spin-offs, but now we're splitting hairs.
Most fantasy Warhammer games do tend to stick to the Old World, however, like Vermintide and Total War: Warhammer, so Storm Ground does still set itself apart. You'll take control of a customisable team of warriors, their roster dependent on the faction, and then upgrade them with new equipment and skills as you slaughter your way through the non-linear campaign. The 3D turn-based fights are all 1v1 affairs, and you'll be able to play solo or online.
Age of Sigmar took over from the Old World and Warhammer Fantasy Battles back in 2015 and just seems to be getting more and more popular—though I'm a 40K boy myself—so it is peculiar that the setting hasn't been mined more. At least that's starting to change.
Storm Ground is coming next year, and further away there's the Age of Sigmar RTS from Frontier. That's not due out until late 2022 at the earliest, unfortunately, and doesn't even have a name.