This example demonstrates how to show a topmost non-modal form, but only within an application. The form must not overlap forms from other applications.
If you use Form.TopMost property, the form will overlap all other non-topmost forms, but also those from other applications. Instead of this, set the Form.Owner property to the parent form – the one which should be under the form (e.g. the main form).[C#]
// use Form.Owner instead of Form.TopMost form1.Owner = mainForm;