Just to add the ones i use, i like notepad stickies for a laptop, and this notepad app for my phone that has a widget that makes it so i can see it on my home screen. You can adjust how transparent the notepad is against your background.
It's not necessarily that I'm losing my memory, but if i trust that i will look at the notepad every day, which i will because its right on my home screen, then for all intents and purposes i can "forget" all that stuff. If i use an alarm, and a calendar, and a notepad - then i feel i can be more mindful and "in the moment" because my brain's RAM is free.