The simplest thing that could possibly work in Tetris (pivotallabs.com)

Writing Tetris inspired by Ward Cunningham: “What’s possible? What is the simplest thing we could say in code, so that we’ll be talking about something that’s on the screen, instead of something that’s ill-formed in our mind. Once we get something on the screen, we can look at it. If it needs to be more, we can make it more.”