Horde - Horde Groupware is a free, enterprise ready, browser based collaboration suite.
Future Me - Send an email to your future self
Roundcube - Web-based IMAP email client
Dabble Me - Your own private place to write. A journal/diary to help you remember what's happened in your life.
Mailo - Mailo is an email client where you can send and receive emails to and from anyone with an email address.
Letter to Yourself - Send a physical letter to your future self