Which of the following tools in Unity is specifically designed to help with initial prototyping?

The ProBuilder package is specifically designed to assist with initial prototyping in Unity. It enables developers to quickly create and manipulate 3D models and environments directly within the Unity interface. This flexibility is essential during the early stages of game development when ideas are still taking shape and rapid iteration is needed. ProBuilder provides an easy-to-use interface for constructing geometry, making it possible to visualize game concepts and test gameplay mechanics without needing to rely heavily on external modeling software.

While other tools listed serve important functions within Unity, they are not primarily focused on prototyping. Animation Rigging is oriented toward creating complex character animations, Unity Analytics provides insights into player behavior and game performance, and Shader Graph is designed for creating and visualizing shaders for enhancing graphics. Each of these serves specific purposes but does not facilitate the rapid conceptual development needed during the prototyping phase like ProBuilder does.