Sketch Mirror - Preview your iOS designs directly on your devices
MJML - The open source framework for responsive emails
Flowkit - Sketch library for user flows/content maps/annotations
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.
Crystal: Sketch Mirror for Android - Crystal: Sketch Mirror for Android is an application that is designed for viewing your sketch designs in real-time, navigate prototypes and download content related to the sketches for offline viewing.
Templates by Email Monster - Hundreds of free, responsive email templates. Pick and edit.