app3.kv

<HeaderButton>:
    background_normal: "red10x10.png"

<SubWindow>:
    WindowHeader:
        orientation: "horizontal"
        size_hint: 1, None
        height: 40
        padding: 5
        spacing: 5
        canvas.before:
            Color:
                rgba: 0.0, 0.0, 0,9, 1.0
            Rectangle:
                pos: self.pos
                size: self.size

        HeaderButton:
            text: "Play"
            size_hint: 1, 1
            on_press: root.play()

        HeaderButton:
            text: "Close"
            size_hint: 1, 1
            on_press: root.close(args[0])
            on_touch_down: root.touch_down(args[0], args[1])

app3.py

from kivy.app import App
from kivy.uix.button import Button
from kivy.uix.floatlayout import FloatLayout
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.label import Label
from kivy.uix.anchorlayout import AnchorLayout
import Overlay

class ButtonOverlay(AnchorLayout, Overlay.Overlay):
    def __init__(self, *args, **kwargs):
        print "++++++++++++++++"
        print "ButtonOverlay"
        super(ButtonOverlay, self).__init__(*args, **kwargs)
        self.button_new=(Button(text="New"))
        self.button_new.bind(on_press=self.new_pressed)
        self.add_widget(self.button_new)

    def new_pressed(self, something):
        print "press: ButtonOverlay: Button 'New'!", something, "RETURN TRUE"
        self.parent_container.add_newthing(something)
        return True

class HeaderButton(Button):
    def __init__(self, *args, **kwargs):
        print "++++++++++++++++"
        print "HeaderButton"
        super(HeaderButton, self).__init__(*args, **kwargs)


class WindowHeader(BoxLayout):
    def __init__(self, *args, **kwargs):
        print "========================================================"
        print "WindowHeader"
        super(WindowHeader, self).__init__(*args, **kwargs)

    def on_touch_down(self, touch):
        print "WindowHeader DOWN"
        super(WindowHeader, self).on_touch_down(touch)

    def close(self):
        print "WindowHeader close"


class SubWindow(BoxLayout):
    def __init__(self, *args, **kwargs):
        print "**********************************************************"
        self.orientation = "vertical"
        self.title = "BIG TITLE"
        super(SubWindow, self).__init__(*args, **kwargs)
        self.button_internal=Button(text="[color=3333ff]Label: " + self.title + "[/color]", markup=True,
                               background_normal="white10x10.png")
        self.add_widget(self.button_internal)
        self.button_internal.bind(on_press=self.press)
        self.button_internal.bind(on_touch_down=self.touch_down)

    def on_parent(self, widget, parent):
        print "SubWindow: Added to parent"

    def play(self):
        print "SubWindow: Play"
        # PalmMediator.play(self.collection)

    def close(self, thingy):
        print "SubWindow: close:", "***" + self.title + "***, my x,y pos:", thingy.x, thingy.y
        print "thingy:", thingy
        print "parent:", thingy.parent
        grandparent = thingy.parent.parent
        print "grandparent:", thingy.parent.parent
        print "root, remove:",
        self.get_root_window().children[0].remove_this(grandparent)
        # remove_this(grandparent)

    def touch_down(self, thingy, touch):
        print "SubWindow: touch_down", "***" + self.title + "***:", thingy.x, thingy.y, thingy.width, thingy.height,\
              "touch coords:", touch.x, touch.y
        print "           touch_down: Parent:", self.parent

    def press(self, thingy):
        print "SubWindow: button_internal: press:", thingy
        print "           parent:", self.parent
        print "    is_triggered?:", self._trigger_layout.is_triggered

class newthing(FloatLayout, Overlay.Overlay):
    def __init__(self, *args, **kwargs):
        super(newthing, self).__init__(*args, **kwargs)
        self.button_new=Button(text='Top', size_hint=(None,None),
                               pos=(50,50), size=(800,200))
        self.add_widget(self.button_new)
        self.button_new.bind(on_press=self.press)
        self.button_new.bind(on_touch_down=self.touch_down)

    def press(self, thingy):
        print "newthing: press", thingy

    def touch_down(self, thingy, touch):
        print "newthing: touch", thingy, touch


class ui(FloatLayout):
    def __init__(self, *args, **kwargs):
        super(ui, self).__init__(*args, **kwargs)
        print "__init__ ui"
        self.internal_layout = BoxLayout(
            orientation='vertical'
        )
        self.add_widget(self.internal_layout)
        self.button_top=Button(text='Top')
        self.button_does_no_thing = Button(text='Does No Thing')
        self.internal_layout.add_widget(self.button_top)
        self.internal_layout.add_widget(self.button_does_no_thing)
        self.button_does_no_thing.bind(on_touch_down=self.touch_down)
        self.button_does_no_thing.bind(on_press=self.press)
        self.overlay = ButtonOverlay(
            size_hint=(None, None),
            # pos_hint={'left': None, 'top': None},
            anchor_x = 'left',
            anchor_y = 'top',
            size=(60, 60)
            # orientation='vertical'
            )
        self.overlay.register(self)

    def press(self, thingy):
        print "ui: press: does_no_thing button:", thingy

    def add_newthing(self, thingy):
        print "ui: add_new_thing", thingy
        self.new_thing=SubWindow()
        self.internal_layout.add_widget(self.new_thing)

    def touch_down(self, thingy, touch):
        print "ui: touch:", thingy, touch
        print "ui: touch: does_no_thing button:", self.button_does_no_thing

    def remove_newthing(self):
        self.internal_layout.remove_widget(self.new_thing)

    def remove_this(self, widget):
        print "SELF:", self, "WANT TO REMOVE:", widget
        print "CHILDREN:"
        print self.children
        self.internal_layout.remove_widget(widget)

    def get_newthing(self):
        return self.new_thing

class App3(App):
    def build(self):
        return ui()

if __name__ == '__main__':
    App3().run()

Overylay.py

from kivy.core.window import Window
from kivy.clock import Clock
from kivy.uix.widget import Widget


class Overlay(Widget):
    def __init__(self, *args, **kwargs):

        self.parent_container = kwargs.pop("registered_parent", None)
        super(Overlay, self).__init__(*args, **kwargs)
        if self.parent_container is not None:
            self.start_fade_timer()
            self.show()
        self.mouse_pos = Window.mouse_pos

    def fade_in_out(self, dt):
        if Window.mouse_pos != self.mouse_pos:
            self.mouse_pos = Window.mouse_pos
            self.idle_ticks = 0
            if self.parent == None:
                self.show()
            return
        if self.idle_ticks > 3:
            self.parent_container.remove_widget(self)
        else:
            self.idle_ticks += 1

    def show(self):
        if self.parent is not None:
            return
        if self.parent_container is not None:
            self.parent_container.add_widget(self)

    def on_touch_move(self, touch):
        super(Overlay, self).on_touch_move(touch)
        self.idle_ticks = 0

    def start_fade_timer(self):
        self.idle_ticks = 0
        self.fader_event = Clock.schedule_interval(self.fade_in_out, 0.25)

    def on_touch_down(self, touch):
        super(Overlay, self).on_touch_down(touch)

    def register(self, container):
        self.parent_container = container
        self.show()
        self.start_fade_timer()

    def unregister(self):
        self.fader_event.cancel()
        if self.parent_container is not None:
            self.parent_container.remove_widget(self)
            self.parent_container = None