Basic usage: inherent from SaintsField.Editor.SaintsEditorWindow

#if UNITY_EDITOR
using SaintsField.Editor;

public class ExamplePanel: SaintsEditorWindow
{

    [MenuItem("Window/Saints/Example/SaintsEditor")]
    public static void OpenWindow()
    {
        EditorWindow window = GetWindow<ExamplePanel>(false, "My Panel");
        window.Show();
    }

    // fields
    [ResizableTextArea]
    public string myString;

    [ProgressBar(100f)] public float myProgress;

    // life-cycle: OnUpdate function
    public override void OnEditorUpdate()
    {
        myProgress = (myProgress + 1f) % 100;
    }

    [ProgressBar(100f)] public float myCoroutine;

    // Layout supported
    [LayoutStart("Coroutine", ELayout.Horizontal)]

    private IEnumerator _startProcessing;

    // Button etc supported
    // EditorCoroutine supported
    [Button]
    public void StartIt()
    {
        StartEditorCoroutine(_startProcessing = StartProcessing());
    }

    [Button]
    public void StopIt()
    {
        if (_startProcessing != null)
        {
            StopEditorCoroutine(_startProcessing);
        }

        _startProcessing = null;
    }

    private IEnumerator StartProcessing()
    {
        myCoroutine = 0;
        while (myCoroutine < 100f)
        {
            myCoroutine += 1f;
            yield return null;
        }
    }

    // Other life-cycle
    public override void OnEditorEnable()
    {
        Debug.Log("Enable");
    }

    public override void OnEditorDisable()
    {
        Debug.Log("Disable");
    }

    public override void OnEditorDestroy()
    {
        Debug.Log("Destroy");
    }
}

#endif

An example of using as a ScriptableObject editor (or any serializable object)

#if UNITY_EDITOR
using SaintsField.Editor;
using SaintsField.Playa;

public class ExampleSo: SaintsEditorWindow
{
    [MenuItem("Window/Saints/Example/ScriptableEditor")]
    public static void OpenWindow()
    {
        EditorWindow window = GetWindow<ExampleSo>(false, "Scriptable Editor");
        window.Show();
    }

    [
        AdvancedDropdown(nameof(ShowDropdown)),
        OnValueChanged(nameof(TargetChanged))
    ]
    public ScriptableObject inspectTarget;

    [WindowInlineEditor]  // this will inline the serialized object editor
    public Object editorInlineInspect;

    private IReadOnlyList<ScriptableObject> GetAllSo() => Resources.LoadAll<ScriptableObject>("");

    private Dropdown<ScriptableObject> ShowDropdown()
    {
        Dropdown<ScriptableObject> down = new Dropdown<ScriptableObject>();
        down.Add("[Null]", null);
        foreach (ScriptableObject scriptableObject in GetAllSo())
        {
            down.Add(scriptableObject.name, scriptableObject);
        }

        return down;
    }

    private void TargetChanged(ScriptableObject so)
    {
        Debug.Log(
quot;changed to {so}");
        editorInlineInspect = so;
        titleContent = new GUIContent(so == null? "Pick One": 
quot;Edit {so.name}");
    }

    [LayoutStart("Buttons", ELayout.Horizontal)]

    [Button]
    private void Save() {}

    [Button]
    private void Discard() {}
}
#endif