An ad lib card game
1000 blank white cards appears to be a free-form card game inspired (loosely) by Uno and others. Not only do you invent your own cards, you can do so continually while playing. Indeed, as there are no additional rules, the cards themselves define the game. Many of the existing cards that others have invented appear to increase or decrease your "score" (but none affect the number of cards that you hold; getting rid of all of your cards does not appear to be an objective either).
Perhaps "toy" is a better word than "game", there not even being a defined objective. I must find some people to try this with some time.
(via mefi)