Habitica - Habitica is a free habit building and productivity application.
HabitBull - HabitBull
Beeminder - Beeminder
Coach.me - Coach.me is a coach that goes everywhere with you, helping you achieve any goal, change any habit, or build any expertise.
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
The HabitHub - The HabitHub