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 Architect - All-in-one system to write, manage and organize email

Todoist - Todoist is a to-do list that helps you get organized, at work and in life.

KanbanMail - A Kanban board for your emails.

Asana - Asana project management is an effort to re-imagine how we work together, through modern productivity software. Fast and versatile, Asana helps individuals and groups get more done.

Clean Email - Clean Email is an online service that empowers you to take control of your mailbox.