I built FriendlyCaptcha over the past 2 months because I was tired of there being no good alternatives to Google's reCAPTCHA and the like that your users won't hate you for.
FriendlyCaptcha is based on proof-of-work (think hashcash): instead the user labeling fire hydrants in images, they commit their device to doing computations for at least a couple of seconds. The idea is that the cost of an attack is not so different for a spammer: instead of running a ML model to label the images (or solve the audio challenge) they would need to solve the proof-of-work challenge. That's probably good enough for most if not all websites, and compares favorably against ReCAPTCHA which has many issues (privacy, accessibility, bundle size & bandwidth, menial tasks, customizability, closed-source).
The attacker shouldn't be able to use much more optimized code, which is where WebAssembly comes in: the FriendlyCaptcha solver is WASM based (with JS fallback) which achieves close to native speeds. The solver [0] and widget [1] are all open source so you can play with it or customize it for your website.
The question is if this is what people want for their website, or maybe what the world needs is just a less evil reCAPTCHA?
In case you missed it on the main website, there is a demo here [2].
[0]: https://github.com/gzuidhof/friendly-pow
[1]: https://github.com/gzuidhof/friendly-challenge
[2]: https://friendlycaptcha.com/demo