Citation needed
One of the most popular ones is Anubis. It uses a proof of work and can even do poisoning: https://anubis.techaro.lol/
They even mention iocaine. I know, inconceivable!: https://iocaine.madhouse-project.org/
There's also tons of HN posts on the topic with varying solutions:
https://news.ycombinator.com/item?id=45935729
https://news.ycombinator.com/item?id=45711094
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I use iocaine[0] to generate a tarpit. Yesterday it served ~278k "pages" consisting of ~500MB of gibberish (and that's despite banning most AI scrapers in robots.txt.)
[0] https://iocaine.madhouse-project.org