* No self-reporting. I can attest this a huge source of friction for users.
* Aligned business model. I also donate 100% of penalties to charity. It's shocking how many accountability apps are incentivized for you to fail.
* External accountability. It's an underrated tool and I'm glad it's gaining more recognition.
However, I think there's also such a thing as too much accountability. Life comes in the way and people won't always hit their goals. When you penalize failure, you penalize trying. Instead, it's better to encourage learning from failure.
That's why I impose compassionate accountability. You're only required to check in on your goals, not succeed at them. This way, you can fight through the problem instead of giving up the moment you fail.
Here's a recent example from Habit Gym that illustrates this quite well. It's a user trying to quit smoking - they start off slow, but pick up momentum quickly because they learned from their mistakes. https://i.imgur.com/1eiZEMy.png
Just my two cents! Good luck with your app!