Draw Something is a Pictionary-style game for iOS and Android that has shown an incredible rate of growth since its launch on February 1st. Developer OMGPOP's CEO Dan Porter told Business Insider that the app has racked up over 20 million downloads in only five weeks — almost as much as Instagram's entire 27 million users, and more than the 15 million Foursquare has managed in over three years. Over a billion pictures have been drawn in the game, with this past Sunday seeing more than 3,000 being sent every second.

It's worth noting that the game is two-player only, so a lot of the downloads will have been the result of encouragement from friends seeking for partners, but that sounds like a good business model to us. Word-of-mouth can be an unbeatable form of advertising, and it's working out for OMGPOP — while the company hasn't spent anything on marketing since launch week, the ad-supported freemium game is apparently generating revenue of six figures by the day.