Recurrr - Send recurring emails
Email Studio for Gmail - Send personalized emails, schedule emails directly in Gmail
Right Inbox - Schedule Emails in Gmail To Be Sent Later
RequestLogic - The marketing tool to help orchestrate email campaigns
SendRecurring - SendRecurring allows you to setup, send, and maintain scheduled email reminders.
Mixmax Sequences - Easy & powerful drip campaigns for Gmail, Inbox & Salesforce