PWNtcha stands for “Pretend We’re Not a Turing Computer but a Human Antagonist”, as well as PWN capTCHAs. This project’s goal is to demonstrate the inefficiency of many captcha implementations.

http://sam.zoy.org/pwntcha/, via BoingBoing.

It still can't solve the Yahoo captchas, though; as it says the Yahoo captcha is “A very good captcha, but not always human-solvable.”

While the complaints against Captcha systens are valid it is unfortunate that there doesn't seem to be a better spam solution at the moment.