Habit21 is an app that provides users a mechanism to create a good habit, or break a bad one. Users either create or join an existing goal, and commit to achieving the goal in 21 days. Example goals include quitting smoking, or going to the gym. The adherence to the goal is judged by two people nominated by the user. If the user fails to achieve the goal, they are charged $5. Users who succeed at their goal are given some money from the users who failed to achieve their goal.