There are a lot of story-based games circling around the pony fandom, but not many have the strong player-influenced dynamic that Shattered Kingdom aims to provide. The project, being developed by a group known as Alicorn Games, is a turn-based strategy RPG centered around an Equestrian civil war between the Celestial Empire and the New Lunar Republic. The game will be heavily story-oriented and non-linear, with the player's actions influencing various story elements throughout the course of the game.
The game is still early in development, and no public demo exists (at least that I can find), but a recent video of their panel at Bronycon 2014 showcases some of the team's current progress. More information can be found on the team's official blog.