Unlayer might be a bit more popular than Polymail. We know about 1 link to it since March 2021 and only 1 link to Polymail. We are tracking product recommendations and mentions on various public social media platforms and blogs. They can help you identify which product is more popular and what people think of it.
Polymail - This one is a lot like Twobird but with a lot more features. It's a different type of email client. It's really cool, but the Windows version is just a web app. It's available on iOS as well. Source: over 2 years ago
Before that we had some luck using RazorLight, but we did all email templates in an editor Unlayer, exported the html and made a layout and view files. Source: about 1 year ago
Airmail - Airmail is a lightweight and lightning fast mail client for Mac.
MJML - The open source framework for responsive emails
Spark Mail - Spark helps you take your inbox under control. Instantly see what’s important and quickly clean up the rest. Spark for Teams allows you to create, discuss, and share email with your colleagues
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.
Thunderbird - Thunderbird is a free email application that's easy to set up and customize - and it's loaded with great features!
BeeFree.io - Bee is MailUp's drag-&-drop editor for responsive design emails.