While many to do and productivity apps load on more and more features, Clear removes them.  It takes the main thing that is desirable about a to do list–the act of checking things off, and makes it satisfying, almost gamifying it.  The app is simple: a few themes, the option to have multiple lists, and a completely gesture-based interface.  I have downloaded many to do list apps, but for now Clear is the only one that has stuck–it’s lack of bells and whistles and simple design make it pleasant to use, and easy to pick up on the go.