ReDo cures a serious lack in the built-in To Do list: the inability to schedule recurring reminders. It adds a powerful and flexible repeat capability to the To Do list program, so that you can set up reminders that automatically insert themselves into your To Do list on any required repeating basis. ReDo can remind you to take out the trash every Thursday, pay your bills on time each month, or start on that sales report 3 business days before the end of each quarter. You can even set an alarm to go off if you haven't checked off a reminder by a specified time. If you use the To Do list (or would, if only it were more powerful), you need ReDo.
I decided to write this utility the first time I had to manually cut & paste a reminder from the Date Book to my To Do list. It's the one feature from my old HP 200LX that I missed the most.