Unity3DKit is a framework which wraps the iOS-Unity3D bridge code in a static library (.framework file).
It provides a set of classes which allow to use a UIViewController which wraps the Unity3D functionality. This allows to utilize Unity3D-powered views in otherwise native UIKit-driven applications.
To achieve something similar on your own you need to spend at least a day or more breaking down the iOS trampoline project Unity comes with – not to mention the need for some advanced Objective-C programming knowledge.
We are thinking about providing Unity3DKit for commercial licensing (via the Asset Store). Please let us know if you would be interested in purchasing it.
Short Video Overview: