The app Draw Something has has more than 50m downloads in 50 days

"Zynga has released a statement that says Draw Something has passed 50 million downloads, making it one of the fastest growing apps of all time. It's likely the only app to ever hit 50 million downloads in just 50 days.
"We believe it’s not only the fastest growing original mobile game of all time – 50 days to hit 50 million downloads - but one of the fastest growing web sensations that we’ve seen.  In addition, the game just regained its spot as the #1 paid app in the App Store, knocking off Angry Birds Space," says Zynga."

Source:  Business Insider, 4th April 2012