Ever wanted a list of Vector3s easily accessible through Unity's inspector window?

PositionListTool.cs

using System.Collections.Generic;
using UnityEngine;

public class PositionListTool : MonoBehaviour
{
    [SerializeField]
    List<Vector3> positions = new List<Vector3>();

    public List<Vector3> GetPositions()
    {
        return positions;
    }

    public Vector3 GetPositionAtIndex(int index)
    {
        return positions[index];
    }

    public void SetPositionAtIndex(int index, Vector3 newVec)
    {
        positions[index] = newVec;
    }

    public void AddNewPosition(Vector3 newVec)
    {
        positions.Add(newVec);
    }

    public int Count()
    {
        return positions.Count;
    }
}

PositionListToolEditor.cs

using UnityEngine;
using UnityEditor;

/// <summary>
/// Put me in a folder called "Editor"
/// </summary>
[CustomEditor(typeof(PositionListTool)), CanEditMultipleObjects]
public class PositionListToolEditor : Editor
{
    SerializedProperty positionArray;

    public static bool hideTransformTool;

    protected virtual void OnSceneGUI()
    {
        PositionListTool myScript = (PositionListTool)target;

        if (myScript.GetPositions().Count > 1) Handles.DrawPolyLine(myScript.GetPositions().ToArray());

        for (int i = 0; i < myScript.GetPositions().Count; i++)
        {
            Undo.RecordObject(myScript, "Changed position");
            myScript.SetPositionAtIndex(i, Handles.PositionHandle(myScript.GetPositionAtIndex(i), Quaternion.identity));
        }

    }

    private void OnEnable()
    {
        positionArray = serializedObject.FindProperty("positions");
        Tools.hidden = hideTransformTool;
    }

    private void OnDisable()
    {
        Tools.hidden = false;
    }

    public override void OnInspectorGUI()
    {
        serializedObject.Update();

        PositionListTool myScript = (PositionListTool)target;

        bool hideTool = EditorGUILayout.Toggle("Hide Transform Tool", hideTransformTool);
        if (hideTool != hideTransformTool)
        {
            hideTransformTool = hideTool;
            Tools.hidden = hideTransformTool;
            if (SceneView.sceneViews.Count > 0) SceneView.lastActiveSceneView.Repaint();
        }

        DrawPropertiesExcluding(serializedObject, new string[] { "m_Script" });

        EditorGUILayout.BeginHorizontal();
        if (GUILayout.Button("Add Position At Local Origin"))
        {
            int index = positionArray.arraySize;
            positionArray.InsertArrayElementAtIndex(index);
            SerializedProperty pos = positionArray.GetArrayElementAtIndex(index);
            pos.vector3Value = myScript.transform.position;
        }

        if (GUILayout.Button("Add Position at World Center"))
        {
            int index = positionArray.arraySize;
            positionArray.InsertArrayElementAtIndex(index);
            SerializedProperty pos = positionArray.GetArrayElementAtIndex(index);

            pos.vector3Value = Vector3.zero;
        }
        EditorGUILayout.EndHorizontal();

        if (serializedObject.hasModifiedProperties)
        {
            serializedObject.ApplyModifiedProperties();
        }
    }
}