Non-opaque application windows in iOS 7, with optional blur. Shows the user's wallpaper under the app, with Parallax if supported.

gistfile1.m

typedef NS_ENUM(NSUInteger, UIBackgroundStyle) {
    UIBackgroundStyleDefault,
    UIBackgroundStyleTransparent,
    UIBackgroundStyleLightBlur,
    UIBackgroundStyleDarkBlur,
    UIBackgroundStyleDarkTranslucent
};

@interface UIApplication (UIBackgroundStyle)
-(void)_setBackgroundStyle:(UIBackgroundStyle)style;
@end

[application _setBackgroundStyle:UIBackgroundStyleDarkBlur];