One of my favourite little hacks is how to add reCAPTCHA to Oracle SSO, which I wrote about last year. I've now finally got around to setting it up with its own sourceforge project.
OssoRecaptcha is a demonstration of integrating the CAPTCHA service from recaptcha.org with Oracle Single-Sign-On. It can be used in production OSSO deployments, and also as an example of integrating any 3rd party authentication system with OSSO.