Wise

Wise makes good use of your fragmented smartphone time. It delivers meaningful small-sized contents (called "cards") to your phone's notification screen so you can read them without even unlocking your phone.

It's a great tool for going over highlights of a book, memorizing key points, or appreciating poems ...

You control what's delivered to you -- you can create the content yourself or find interesting "decks" shared by others. Once you turn on the notification of a deck, its cards will be delivered to you once in a while in a quiet way.