SendRecurring - SendRecurring allows you to setup, send, and maintain scheduled email reminders.
Salesflare - Simply powerful CRM. Automates your data to build better relationships and make more sales.
Recurrr - Send recurring emails
Onesheet CRM - The Simple CRM for Google Sheets
Followup.cc - FollowUp for email is a lightweight productivity suite that keeps your conversations and tasks from slipping through the cracks. Set perfectly timed reminders that arrive at the top of your inbox, right when you need them.
Dex - One place for your relationships — impress with thoughtfulness