Zendesk Support Suite - Zendesk Support Suite is a tool that solves and emerges multiple tasks in one place.
Right Inbox - Schedule Emails in Gmail To Be Sent Later
Gmelius - Gmelius is the first collaboration platform designed for G Suite and your company's daily tools.
Recurrr - Send recurring emails
Google Voice - Google Voice gives you one number for all your phones, voicemail organized in an email format, free...
FollowUpThen - The simplest way to schedule an email reminder