Snow Effect. CAEmitterLayer demo.
It's a simple class derived from UIView:
@interface SnowEmitterView : UIView
- (void)start;
- (void)stop;
@end
Just add it to your view:
CGRect bounds = [[self view] bounds];
SnowEmitterView *viewSnow = [[SnowEmitterView alloc] initWithFrame:bounds];
[[self view] addSubview:viewSnow];
[viewSnow start];