So your idea is perfect if you want to do a challenge by yourself, and is something we're definitely considering adding in the future! Because in our model, a challenge needs at least 2 people. So if we want to support a single person challenge in the future, we'd want to implement something like giving away to charity or something else, exactly like you said!

I'll probably build this eventually. Let me know if this is open source, I'd be down to implement it. It looks like you're using PHP/Symfony, so this is right down my alley.

I think sending the money lost on funds to charities makes more sense as sharing the money on the pot among the ones who succeed could result in bad actors trying to exploit the system by always checking their goals as completed.

By sending lost money to charities you eliminate the positive reward factor of the game (which is the main incentive for exploiters).