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
TaskPaper - Plain text to-do lists for Mac
Nirow - Habit tracking: Automated, Siri-ed, Calendar-ed, and More!
Microsoft To-Do - Task management tool
Things - Things is an easy to use task manager.