Caliburn.Metro

  //Basic AppBootstrapper
  public class AppBootstrapper : CaliburnMetroCompositionBootstrapper<AppViewModel>
  {

  }
    
  //AppWindowManager with custom Main window
  [Export(typeof(IWindowManager))]
  public class AppWindowManager : MetroWindowManager
  {
      public override MetroWindow CreateCustomWindow(object view, bool windowIsView)
      {
          if (windowIsView)
          {
              return view as MainWindowContainer;
          }

          return new MainWindowContainer
          {
            Content = view
          };
      }
  }

//Autofac AppBootstrapper
public class AppBootstrapper : CaliburnMetroAutofacBootstrapper<AppViewModel>
{
    protected override void ConfigureContainer(ContainerBuilder builder)
    {
        builder.RegisterType<AppWindowManager>().As<IWindowManager>().SingleInstance();
        var assembly = typeof(AppViewModel).Assembly;
        builder.RegisterAssemblyTypes(assembly)
            .Where(item => item.Name.EndsWith("ViewModel") && item.IsAbstract == false)
            .AsSelf()
            .SingleInstance();
    }
}

//AppWindowManager with custom Main window
public class AppWindowManager : MetroWindowManager
{
    public override MetroWindow CreateCustomWindow(object view, bool windowIsView)
    {
        if (windowIsView)
        {
            return view as MainWindowContainer;
        }
        return new MainWindowContainer
        {
            Content = view
        };
    }
}