I built a service reminder web application for my client( full stack Vehicle Location service). Unfortunately they could never get their customers who had requested this to use the application. That appears to be the hardest part of any To-Do list software: getting the people who need it to use it.
The deskpad of the Planner Pad system (in post 18) sits on top of your desk so that you can’t ignore it or forget to use it. (Well, you can ignore it, but the blank page or list of long undone items is a stark reminder, LOL.)