InStream CRM - Business relationship management platform - CRM alternative
SendRecurring - SendRecurring allows you to setup, send, and maintain scheduled email reminders.
Gmail CoPilot by cloudHQ - Easy CRM: View all past conversations with an email contact
Recurrr - Send recurring emails
Crmble - Easy peasy crm for Trello
FollowUpThen - The simplest way to schedule an email reminder