If No Reply - Simple email automation that works for Gmail
SendRecurring - SendRecurring allows you to setup, send, and maintain scheduled email reminders.
Assistant.to - GoToMeeting. Put your GoToMeeting link in the Assistant. to "Location" field. Once the recipient selects a time, you will both receive an invite with a unique GoToMeeting link.
Recurrr - Send recurring emails
SendLater - Email scheduler for Mac Mail.
FollowUpThen - The simplest way to schedule an email reminder