EmailPlayground - EmailPlayground provides solution to schedule and send emails with ease.
Right Inbox - Schedule Emails in Gmail To Be Sent Later
Email Studio for Gmail - Send personalized emails, schedule emails directly in Gmail
Seventh Sense - Seventh Sense helps marketers and sales professionals reach the people that make them successful using artificial intelligence powered email.
If No Reply - Simple email automation that works for Gmail
LetterMeLater.com - LetterMeLater.com allows you to send emails to anyone, with the ability to have them sent at any future date and time you choose.