I found that by simply installing a free calendar app on my smartphone or tablet, I never forgot another event of any kind. They are very intuitive and allow you to set reminders of the appointment at your chosen intervals. They also pop the event up on your screen when you first turn your tablet or phone on, which takes care of the problem for me. I would recommend just putting the calendar on the device you use most consistently, as maintaining two is cumbersome. You might also want to check reviews of the app you are considering, before installing. In this way you can find the features that appeal to you most, and avoid apps that have demonstrated problems.