Initial version.

main.py

@@ -0,0 +1,74 @@
+#!/usr/bin/env python3
+
+import sys
+import gi
+
+gi.require_version("Gtk", "4.0")
+gi.require_version('Polkit', '1.0')
+
+from gi.repository import Gtk, Polkit, GObject, Gio
+
+class MainWindow(Gtk.Window):
+    def __init__(self, title, width, height, application=None):
+        super().__init__(title=title, application=application)
+
+        task_list = Gtk.ListBox()
+        self.set_child(task_list)
+
+        row = Gtk.ListBoxRow()
+        hbox = Gtk.Box(spacing=6)
+        button = Gtk.Button.new_with_label("Click Me")
+        button.connect("clicked", self.on_click_me_clicked)
+        hbox.append(button)
+        row.set_child(hbox)
+        task_list.append(row)
+
+        row = Gtk.ListBoxRow()
+        hbox = Gtk.Box(spacing=6)
+        button = Gtk.Button.new_with_mnemonic("_Open")
+        button.connect("clicked", self.on_open_clicked)
+        hbox.append(button)
+        row.set_child(hbox)
+        task_list.append(row)
+
+        row = Gtk.ListBoxRow()
+        hbox = Gtk.Box(spacing=6)
+        button = Gtk.Button.new_with_mnemonic("_Close")
+        button.connect("clicked", self.on_close_clicked)
+        hbox.append(button)
+        row.set_child(hbox)
+        task_list.append(row)
+
+    def on_click_me_clicked(self, button):
+        print('"Click me" button was clicked')
+
+    def on_open_clicked(self, button):
+        print('"Open" button was clicked')
+
+    def on_close_clicked(self, button):
+        print("Closing application")
+        self.close()
+
+
+class Application(Gtk.Application):
+    """ Main Aplication class """
+
+    def __init__(self):
+        super().__init__(application_id='com.codigoparallevar.gtk4-organizer',
+                         flags=Gio.ApplicationFlags.FLAGS_NONE)
+
+    def do_activate(self):
+        win = self.props.active_window
+        if not win:
+            win = MainWindow("My Gtk4 Application", 800, 800, application=self)
+        win.present()
+
+
+def main():
+    """ Run the main application"""
+    app = Application()
+    return app.run(sys.argv)
+
+
+if __name__ == '__main__':
+    main()