Nikatime - A Slackbot that keeps track of what your team is doing so you don't have to.
Future Me - Send an email to your future self
Exstora - Built-in quick note: save ideas, contacts, interesting facts
Dabble Me - Your own private place to write. A journal/diary to help you remember what's happened in your life.
OneNote Online - OneNote Online, part of Office Online, is the online version of Microsoft OneNote.
Letter to Yourself - Send a physical letter to your future self