Some great points there. Did not think of sending someone you don't like a message... could be very effective indeed.

The main part I am struggling with for this project idea is how to keep people honest. I used Beeminder for a while, but as it was easy to tell them to cancel the payments, I switched from honesty to finding excuses for not having done a certain task. Then I gave up using it as it was not doing what I needed.

Best usecases for me were the ones where it was basically calling a third-party app to check if I had done the task, such as Strava or Google Fit to check if I had done a certain amount of steps. Even though one can still game those, i did not feel the need to.