From iPhone Development Wiki

OBButtonTray is a UIView subclass in OnBoardingKit.framework.

It can contain multiple buttons as well as a "caption label", a small UILabel usually reserved for legal text.

An instance of OBButtonTray is automatically created during the initialization of an OBWelcomeController and can be accessed from the latter.

Adding caption text

[buttonTray addCaptionText:@"This text is really small!"];