“20Q.net is an experiment in artificial intelligence. The program is very simple but its behavior is complex. Everything that it knows and all questions that it asks were entered by people playing this game. 20Q.net is a learning system; the more it is played, the smarter it gets.”
It allows you to play for free in different languages: English, Spanish, French, Italian, German just to mention a few. I had a go yesterday and it is not only fun but good practice for vocabulary and question formation.