Thought Plan - Super convenient tool to write down your thoughts & ideas
Future Me - Send an email to your future self
Taky - Write ideas down as fast as they come up.
Letter to Yourself - Send a physical letter to your future self
Writtens - Quora for writers, ask questions and get advice.
Letter to my future self - Letter to my future self is a prominent email scheduling service that gives you the opportunity to create a letter with goals and thoughts for your future self and schedule a date for sending it.