Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
Sortd - Rated the #1 App for Gmail
Plan - Plan is a better way to organize.
KanbanMail - A Kanban board for your emails.
Tasks - The new task app from the team that brought us Wunderlist, Microsoft To-Do is a great way to manage tasks. List everything you need to do—or import tasks from Outlook, Todoist, and Wunderlist so you don't have to start over.
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.