Daylio - Daylio enables you to keep a private diary without having to type a single line.
Future Me - Send an email to your future self
Penzu - Keep all of your thoughts in one place using Penzu. The app is similar to a journal that you might write in but with a few modern touches that allow you to do everything from sending messages to decorating the pages.
Dabble Me - Your own private place to write. A journal/diary to help you remember what's happened in your life.
Journey - A diary that keeps your private memories forever.
Letter to Yourself - Send a physical letter to your future self