Twilio - Brings voice and messaging to your web and mobile applications.
Stripo - Stripo is an all-in-one email design platform. We enable our clients to build emails of any complexity, including interactive AMP emails, really fast and easy.
Nexmo - Nexmo is a simple two way SMS API with global reach and wholesale rates
MJML - The open source framework for responsive emails
Clockwork SMS - Clockwork is an Easy Text Message API. An SMS API for Developers. Build powerful apps and include SMS. Signup is free, Try it now.
Templates by Email Monster - Hundreds of free, responsive email templates. Pick and edit.