Mosaico.io - Outstanding opensource email template editor by VOXmail.it
Twilio - Brings voice and messaging to your web and mobile applications.
Topol.io - Create professional Email templates easily - Drag & Drop Email Builder.
MessageBird - Reach 7 billion phones in seconds via SMS, Chat & Voice. Try it for free and improve your communication.
BeeFree.io - Bee is MailUp's drag-&-drop editor for responsive design emails.
Nexmo - Nexmo is a simple two way SMS API with global reach and wholesale rates