Hello Guys,
I found some newsletter templates with some cool layout editor or theme builder.

Samples from different developers;

***emailmad.com/template_assets/tytan/preview/
***themeforest.net/item/exim-email-template-with-layout-editor/full_screen_preview/6896699
***templatemine.net/themeForest/robbiewilliams/Seed/LayoutEditor_set02/LayoutEditordemo/demo.html

Does anybody know what library or script they use to achieve this? It seems most themeforest developers are using it! It seems trending for newsletter template world.

All I need to know is the framework or script to use for the theme builder/layout editor.

Any suggestions would be greatly appreciated.

Thank you in advance!