On captchas:

https://m.primal.net/HIju.webp

By attaching real cost to (pseudonymous) identities.

“Real cost makes spam bots uneconomical and disincentivizes antisocial behavior."

https://dergigi.com/2022/12/18/a-vision-for-a-value-enabled-web/

A tiny Lightning payment instead if paying with your attention and time.