If you want a Layer2 plasma with similar guarantees to Ethereum (account based, not zero knowledge) then you may like Gluon.network once they roll out EVM support.
Much of the basis for James Clear’s Atomic Habits is based on and references BJ Fogg’s research at Stanford.
As I see it, James forked Tiny Habits to make it more marketable and has had great success selling books and courses under the Atomic Habits brand.
BJ opted to provide his Tiny Habits materials and 5 day course for free as it generated more data points to support his research.
Having now read both books, I certainly appreciate the plain spoken / matter of fact style of Tiny Habits compared to Atomic Habits which felt more hyped.
A bloom filter of my contact’s phone numbers that is updated on my device and checked on the server could be a good privacy approach. A small number of false positives (robo calls getting through) would be acceptable if the device still filters or presents the option to accept.
PINs could also be a bloom filter on the server, then the device filters on whether the specific PIN entered was single use or has been revoked.