SendRecurring - SendRecurring allows you to setup, send, and maintain scheduled email reminders.
Roundcube - Web-based IMAP email client
Recurrr - Send recurring emails
Mailo - Mailo is an email client where you can send and receive emails to and from anyone with an email address.
FollowUpThen - The simplest way to schedule an email reminder
Mailpile - Mailpile is a modern, fast web-mail client with user-friendly encryption and privacy features.