Remember The Milk - Remember The Milk is a task and time management application for mobile devices.
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
TimePanic - TimePanic is an award-winning application for tracking time spent at the computer.
Taskade - Make lists, organize your thoughts, and be inspired to get things done. Taskade is a collaborative space for your tasks.
WinMilk - WinMilk is a Windows Phone client for the to-do list service 'Remember the Milk'.
Plan - Plan is a better way to organize.