What are some alternatives?
When comparing Responsive Email and Adapti, you can also consider the following products
Responsive View - Test your responsive design across different devices
The Adventures of UX Hero - The world’s first User Experience comic series
SlideRule UX Design Path - Curriculum of Online Courses To Learn UX Design
Am I Responsive - see your website in multiple screen resolutions
SmashBack - Combined, automated inbox for email and app store reviews.
Responsive Viewer - View multiple screen dimensions in one view