Disney Fairies Fashion Boutique is an app based off of Pixie Hollow Online, where you can run a boutique with your online fairy and sell outfits to customers. The app altogether consists of mini games, a shop to customize your boutique (apperance, size, mannequins, etc.), customers to sell outfits to, patterns to unlock, and more.
The app is scheduled to delete around the time of Pixie Hollow (online game)'s closing. This means the app will no longer be available for future downloads, but will still be available for ones with the app at that time, with "limited features".
DFFB is only available on Apple devices, iPhones, iPads, and iPods (supports most versions). There are no plans to make it available for any other mobile devices. It is only available in the American "App Store".