Flow-e is a visualization layer on top of your Gmail or Outlook inbox. It provides an elegant Kanban-like workflow that's combined with the ideas behind Inbox Zero and GTD. Flow-e eliminates the need of external task management tools and transforms your inbox into a central To Do app.
SendRecurring - SendRecurring allows you to setup, send, and maintain scheduled email reminders.
Sortd - Rated the #1 App for Gmail
Recurrr - Send recurring emails
Drag for Gmail - Transform Gmail into organized To Do lists (like Trello)
FollowUpThen - The simplest way to schedule an email reminder
KanbanMail - A Kanban board for your emails.