Despite a few recent setbacks Snapchat’s popularity continues to grow, but for anyone using Windows Phone there’s still no way to officially join in on the photo-sharing fun. It’s another classic example of Microsoft’s crippling app gap, which has hobbled the company from making much progress with its third-place mobile operating system. Now Microsoft is taking matters into its own hands with WindUp, a new Snapchat knockoff that’s just for Windows Phone.