SendLater VS OffHours for Outlook

Recurrr - Send recurring emails

RGB Technologies - Email Scheduler - Email Scheduler provides an intuitive email scheduling solution, integrated within the existing Salesforce account.

Right Inbox - Schedule Emails in Gmail To Be Sent Later

SendRecurring - SendRecurring allows you to setup, send, and maintain scheduled email reminders.

SndLatr - SndLatr is a Gmail plugin that makes it easy to schedule emails to be sent automatically at a later time.

GMass - GMass allows you to easily schedule emails, send out mass emails and mail merge campaigns and more with Gmail! Click here to learn about more features!