HTMLEmail.io - Responsive HTML email templates for startups & developers
Sortd - Rated the #1 App for Gmail
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.
KanbanMail - A Kanban board for your emails.
Startup Emails - Responsive HTML email templates for startups
Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.