Overlap.py

from kivy.config import Config

# Set your maxfps like this:
Config.set('graphics', 'maxfps', 5)

from kivy.app import App
from kivy.lang import Builder
from kivy.uix.screenmanager import ScreenManager, Screen, NoTransition

Builder.load_string("""
<MenuScreen>:
    BoxLayout:
        orientation: 'vertical'

        canvas:
            Color:
                rgb: 0, 0, 0
            Rectangle:
                size: self.size

        Label:
            text: 'foo'
            font_size: 120
        Button:
            on_press: root.manager.current = 'settings'
            text: 'Goto bar'

<SettingsScreen>:
    BoxLayout:
        orientation: 'vertical'

        canvas:
            Color:
                rgb: 0, 0, 0
            Rectangle:
                size: self.size

        Label:
            text: 'bar'
            font_size: 80
        Button:
            text: 'Back to foo'
            on_press: root.manager.current = 'menu'
""")

# Declare both screens
class MenuScreen(Screen):
    pass

class SettingsScreen(Screen):
    pass

# Create the screen manager
sm = ScreenManager(transition=NoTransition())
sm.add_widget(MenuScreen(name='menu'))
sm.add_widget(SettingsScreen(name='settings'))

class TestApp(App):

    def build(self):
        return sm

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