My friends and I run a yearly bicycle scavenger hunt and this year it was up to my wife and me to plan it. One of the problems we always face is predictability. Each hunt can be easily planned out ahead of time by the participants, who then just go from place to place in order. I wanted to break that.
My idea was a system that only gave one question to solve at a time. When you answer the question, you get some points and the next question. To achieve this, I wrote a Ruby on Rails app that ties in with Twilio, allowing anyone with a cellphone to join teams, participate in answering questions and get ridiculed by me behind the scenes.
Check out The Hunt, which is fully open sourced and accepting of comments & criticism.