Streaks - The to-do list that helps you form good habits.
Simpli - Keep track of email, calendars, notes and more in a unified interface.
Taskful - Deadlines, meet your match.
RescueTime - Time management software that shows you how you spend your time & provides tools to help you be more productive.
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
ToDoList - Windows desktop application to stay on top of your daily tasks.