My pops gives us 6 month challenges, based on the scripture in the New Testament describing Jesus growing in wisdom (intellectual) and stature (physical) and in favor with God (spiritual) and man (social/service).

We set goals for each category, and he offers us 50$ per goal achieved for a total of 200$ that we can earn. He makes us spend it on something we wouldn’t otherwise get (not paying back school loans, etc).

Previously just did it with him and my mom and his kids (two of us in mid 30s and our spouses). Recently opened it up to his grandkids, albeit with a smaller fiscal incentive. The money isn’t all that important but we share goals with each other, keep ourselves accountable and it is fun and worthwhile.