TWiki E-mail Reminders
This plugin allows the user to set up e-mail reminders of events.
In our case, we're using this feature in conjunction with our task-tracking system to send reminder emails about tasks at defined increments of time away from the task's due date. The reminder emails tell the user when a task is due in two weeks, one week, two days, tomorrow, today, or overdue. After the task becomes overdue, the reminders come once a day until it is marked complete.
But this plugin can also be used on its own to set up any necessary e-mail reminders, for example, to remind users of birthdays.
Click the image below for larger screenshot.