Question

How could I copy the slide down effect with the tail on the springboard which occurs when a ‘appgroup’ (collection of apps in one folder) is selected?

It would be used to show a few buttons.

Answer 1

You can use simple Core animations to do that.
Like so:

[UIView beginAnimations:nil context:nil];

[UIView setAnimationDuration:2];

coverView.center = CGPointMake(coverView.center.x, 400);

[UIView commitAnimations];

Where coverView is a view covering your buttons, when this animation is executed the view animates to the point X=x Y=400 and uses 2 seconds to do it. You can do this to any object in interface builder, and therefore you can experiment and create what suits you.
Hope that helps.