Rotate.cs

using HoloToolkit.Unity.InputModule;
using UnityEngine;
using IInputHandler = HoloToolkit.Unity.InputModule.IInputHandler;
using IManipulationHandler = HoloToolkit.Unity.InputModule.IManipulationHandler;

public class Rotate : MonoBehaviour, IInputHandler, IManipulationHandler
{
    private IInputSource currentInputSource = null;
    private uint currentInputSourceId;

    public void OnInputDown(InputEventData eventData)
    {
        currentInputSource = eventData.InputSource;
        currentInputSourceId = eventData.SourceId;
        InputManager.Instance.PushModalInputHandler(gameObject);
        InputManager.Instance.RaiseManipulationStarted(currentInputSource, currentInputSourceId, transform.position);
    }

    public void OnInputUp(InputEventData eventData)
    {
        InputManager.Instance.RaiseManipulationCompleted(currentInputSource, currentInputSourceId, transform.position);
        InputManager.Instance.PopModalInputHandler();
    }

    public void OnManipulationCanceled(ManipulationEventData eventData)
    {
    }

    public void OnManipulationCompleted(ManipulationEventData eventData)
    {
    }

    public void OnManipulationStarted(ManipulationEventData eventData)
    {
    }

    public void OnManipulationUpdated(ManipulationEventData eventData)
    {
        float multiplier = 1.0f;
        float cameraLocalYRotation = Camera.main.transform.localRotation.eulerAngles.y;

        if (cameraLocalYRotation > 270 || cameraLocalYRotation < 90)
            multiplier = -1.0f;

        var rotation = new Vector3(0, eventData.CumulativeDelta.x * multiplier);
        transform.Rotate(rotation * 10, Space.World);
    }
}