Referral Roulette
This was a 24 hour coding challenge project I did back in 2011, before I went away to college. Its purpose was to allow users to accumulate points by watching referrals to sites. After enough points, they're able to add their own ads linking to their referral sites. It was a very basic site with no user accounts. It was written in PHP and got quite a several million page hits during its peak. I've since sold the domain off to someone else who has now launched their own iteration of the site.