Clean Email - Clean Email is an online service that empowers you to take control of your mailbox.
Future Me - Send an email to your future self
Hiver - Manage Customer Support, Sales and Projects right from your Gmail inbox. Collaborate with Shared Labels, Shared Contacts, email notes, email reminders and email templates
Letter to Yourself - Send a physical letter to your future self
MailClark - The Slack bot for external communications
Dabble Me - Your own private place to write. A journal/diary to help you remember what's happened in your life.