Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
Streaks - The to-do list that helps you form good habits.
Remember The Milk - Remember The Milk is a task and time management application for mobile devices.
Taskful - Deadlines, meet your match.
Workflowy - A better way to organize your mind.
TickTick - TickTickis a cross-platform to-do list app & task manager helps you to get all things done and make life well organized.