lockrMail - Email on your terms - never give out your personal email ever again
Sortd - Rated the #1 App for Gmail
Polymail - Native email app for email productivity.
KanbanMail - A Kanban board for your emails.
HEY - Email at its best, new from Basecamp.
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.