Calendar
For people who need help keeping track of various dates and tasks that come up in life and reduce the chance of being caught off guard by an unknown event.
The iOS and Android Calendar apps might look different but they offer the same basic uses of tracking dates and scheduling events/appointments. These apps can even remind you when events/appointments are happening and even note the locations of where they will take place. Calendar apps already come pre-installed into all smartphones and tablets, so try to make best use of them.