Nexmo - Nexmo is a simple two way SMS API with global reach and wholesale rates
SendRecurring - SendRecurring allows you to setup, send, and maintain scheduled email reminders.
MessageBird - Reach 7 billion phones in seconds via SMS, Chat & Voice. Try it for free and improve your communication.
Recurrr - Send recurring emails
Plivo - Plivo simplifies your customer engagement.
FollowUpThen - The simplest way to schedule an email reminder