CustomCallout is a project mainly written in OBJECTIVE-C and C, it's free.
Clone of UICalloutView without use of private APIs
This is a custom control that you can use to emulate the look and feel of Apple's UICalloutView, without using any private APIs.
All the basic functionality, correct placement on the screen, support for Retina.
CustomCallout* cc = [[CustomCallout alloc] initWithAnchor:p text:@"Test Callout!" delegate:self param:sender];
[cc showWithAnimationInParent:self.view];
[cc release];
CustomCallout is released under MIT License.