Sortd - Rated the #1 App for Gmail
KanbanMail - A Kanban board for your emails.
Clean Email - Clean Email is an online service that empowers you to take control of your mailbox.
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.
Email Design System Playbook - Learn to design emails faster with a design system
Gmelius - Gmelius is the first collaboration platform designed for G Suite and your company's daily tools.