OptiMonk - OptiMonk is the most powerful Onsite Retargeting platform, that helps you increase the conversion rate of your site, and get more leads by recovering lost visitors.
HTMLEmail.io - Responsive HTML email templates for startups & developers
Elementor Popup Builder - Design-oriented popup builder, built into Elementor
Templates by Email Monster - Hundreds of free, responsive email templates. Pick and edit.
POPUPSMART - A no-code tool to increase e-commerce sales, build email lists and engage with your visitors in just 5-minutes.
MJML - The open source framework for responsive emails