What about this open-source Cloudflare alternative: https://gitgud.io/fatchan/haproxy-protection/ ?
Discussion
Seems like a nice alternative to recaptcha I have to find a site running it to see it in action get a feel to determine. Thanks for letting me know about this i'll have to pass this along & get some feedback from others about it.
Do you have a site which is running this?
I am not using it myself but kiwifarms uses it, so I believe it works good enough to protect heavily targeted websites from DDoS attacks