[ksymph]

I run into https://www.hcaptcha.com/ and https://friendlycaptcha.com/ from time to time as a user without complaint. Can't speak to the latter but I've used the former a bit and it does the job.

[BloodyIron]

Any chance for something 100% self-hostable? hcaptcha and friendlycaptcha last I checked require interfacing with their services.

[Velocifyer]

hCaptcha is horrible. I think that a PoW captcha would be effective to make spammers just mine Monero instead.