doo - A smart, simple app for reminders and to-dos
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
Purp - A smart to-do list and goal tracker app
Remember The Milk - Remember The Milk is a task and time management application for mobile devices.
Gone - An ephemeral to-do list
Workflowy - A better way to organize your mind.