Flow-e is a visualization layer on top of your Gmail or Outlook inbox. It provides an elegant Kanban-like workflow that's combined with the ideas behind Inbox Zero and GTD. Flow-e eliminates the need of external task management tools and transforms your inbox into a central To Do app.
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
KanbanMail - A Kanban board for your emails.
Any.DO - The #1 task management app used by over 11 million people globally, Any.do is your free mobile and online task manager for Android, iPhone, Web and more.
Sortd - Rated the #1 App for Gmail
Microsoft To-Do - Task management tool
Drag for Gmail - Transform Gmail into organized To Do lists (like Trello)