Habitica is a fun and enjoyable way to develop good habits and get things done. Three of us in our family have been "playing" it for a few months now and we enjoy going on quests and encouraging each other. The most fun way to track To Do items that I have found.
This iOS version lets you do almost all of the key things that you can do on the website.
Shadallark about Habitica: Gamified Taskmanager, v1.0.2