Plan - Plan is a better way to organize.
Sortd - Rated the #1 App for Gmail
Realworld - A comprehensive platform to make adulting easier
KanbanMail - A Kanban board for your emails.
Purp - A smart to-do list and goal tracker app
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.