I built a sticky note app you never have to open
I kept losing thoughts in the gap between thinking them and unlocking my phone. So the note lives in the notification shade.
Pull the shade down, type it, done. Grocery list, a reminder, a name you do not want to forget. You do not open the app.
If you write something like "milk, eggs sunday 6pm" it becomes a checklist and sets the reminder for you.
No ads. Free. Nothing to buy later. I did not want to ship something that nags you.
It is called Slip.
Play: https://play.google.com/store/apps/details?id=com.polyhistor.slip