Remember The Milk is an online application that I use to maintain the lists of tasks I need to complete. I can assign a date-time to each task on or by when I want to complete it. But, most of the time when I open RTM what I want to see are the tasks (across all my lists) that are due for completion today. This includes tasks which are overdue.
RTM supports smart lists i.e., virtual lists that are the result of applying certain search operations on the tasks in the actual lists. To get a smart list of all the tasks due today and are also overdue, use the operation