21habit lets users enter goals they want to achieve in 21 days. It then helps you track your progress day-to-day.
This is a side project by a bunch of Amazon and Microsoft engineers. Obviously they have time on their hands, enough to divert attention away from the ongoing mobile battlefield that Microsoft is losing.
The most interesting aspect of the service is it’s charity integration. You pay $21 upfront which you receive back incrementally if you make your daily goals. If you don’t, a dollar goes to charity. Smart.