Templates by Email Monster - Hundreds of free, responsive email templates. Pick and edit.
productboard - Beautiful and powerful product management.
MJML - The open source framework for responsive emails
ProdPad - ProdPad helps your team gather ideas, surface the best ones and turn them into product specs, and then put it all on a product roadmap.
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.
ProductPlan - Cloud-based product roadmap software solution