Every day the site asks one open question ("Name a month people love", etc.). Then you do two things: Guess what the most common answer was yesterday, and answer today's question. Tomorrow's puzzle is built from whatever everyone actually typed today (except for day 0 of course, these are made up). So the game generates its own content and you are playing against the player base.

I also do some simple answer normalization using plural folding, article stripping and a synonym table (fridge/refrigerator). It's still imperfect, feedback appreciated.