Habitica - Habitica is a free habit building and productivity application.
GoalsWon - Human accountability coaching for busy people
LifeRPG - Automatically prioritize your goals and gain XP for achieving them. Features:
CARROT - Meet CARROT, the to-do list with a personality.
Coach.me - Coach.me is a coach that goes everywhere with you, helping you achieve any goal, change any habit, or build any expertise.
Beeminder - Beeminder