Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.

Purp - A smart to-do list and goal tracker app

Asana - Asana project management is an effort to re-imagine how we work together, through modern productivity software. Fast and versatile, Asana helps individuals and groups get more done.

Nirow - Habit tracking: Automated, Siri-ed, Calendar-ed, and More!

Todoist - Todoist is a to-do list that helps you get organized, at work and in life.

Things - Things is an easy to use task manager.