You've played 20 questions, haven't you? This page, the sample application from the IBM developerWorks tutorial Creating an AJAX Mindreader Application with E4X and Prototype, is a Javascript rendition of the game that not only appears to read your mind, but also gets better at it as you go along. For example, to start with we have only 4 items programed into the knowledgebase, but every time the routine guesses wrong, you can teach it about a new object, which it will know for next time you run it.