RGB Technologies - Email Scheduler - Email Scheduler provides an intuitive email scheduling solution, integrated within the existing Salesforce account.
SendLater - Email scheduler for Mac Mail.
ifttt - IFTTT puts the internet to work for you. Create simple connections between the products you use every day.
Right Inbox - Schedule Emails in Gmail To Be Sent Later
Zapier - Connect the apps you use everyday to automate your work and be more productive. 1000+ apps and easy integrations - get started in minutes.
SndLatr - SndLatr is a Gmail plugin that makes it easy to schedule emails to be sent automatically at a later time.