Download the 25 Billionth Apple App Store App and Win a $10,000 Gift Card
"As of today, nearly 25 billion apps have been downloaded worldwide. Which is almost as amazing as the apps themselves. So we want to say thanks. Download the 25 billionth app, and you could win a US$10,000 App Store Gift Card. Just visit the App Store and download your best app yet," Apple explains.
There's an alternate way to enter that doesn't require making a purchasing or downloading/installing an app. You can fill out Apple's Alternate Entry Form up to 25 times per day (the same limit applies to eligible entries from downloaded apps). Timing here is also critical, as the winner of the gift card will either be the person who downloads the 25 billionth app or from "the receipt of the non-purchase entry after the download of the 24,999,999,999th app, which ever comes first," Apple says.
You can read the official rules here.