EditMesh.cs

using UnityEngine;
using UnityEditor;
using System.Collections;

// Super simple/crappy MeshEditor by Alec Holowka http://infiniteammo.ca

[CustomEditor (typeof(Transform))]
public class EditMesh : Editor
{
    public Mesh mesh;
    public Transform targetTransform;

    void OnEnable()
    {
        targetTransform = (Transform)target;
        MeshFilter meshFilter = targetTransform.GetComponent<MeshFilter>();
        if (meshFilter)
        {
            mesh = meshFilter.sharedMesh;
        }
    }

    void OnSceneGUI()
    {
        if (mesh)
        {
            bool meshChanged = false;
            int c = 0;
            foreach (Vector3 vertex in mesh.vertices)
            {
                Vector3 originalPosition = targetTransform.TransformPoint(vertex);
                //Vector3 newPosition = Handles.PositionHandle(originalPosition, Quaternion.identity);
                Vector3 newPosition = Handles.FreeMoveHandle(originalPosition, Quaternion.identity, 0.05f, Vector3.zero, Handles.CircleCap);
                if (newPosition != originalPosition)
                {
                    Vector3[] vertices = mesh.vertices;
                    vertices[c] = targetTransform.InverseTransformPoint(newPosition);
                    mesh.vertices = vertices;
                    meshChanged = true;
                    break;
                }
                //Handles.CubeCap(c, targetTransform.TransformPoint(vertex), Quaternion.identity, 0.05f);
                c++;
            }

            if (meshChanged)
            {

            }
        }
    }
}