During the I/O Keynote, Google announced that it's reached 20 billion Android app installs in the Play Store. In total, 600,000 apps and games are available, with free apps in 190 countries and paid ones in 132. In-app purchases are also a large and lucrative part of sales: 50 percent of revenue apparently comes from billing within apps. Google's still trailing Apple in download numbers here: at WWDC, Apple said it had 30 billion app downloads since the launch of its store in 2008. The total number of apps and games, however, is much closer: Apple announced 650,000 earlier this month. The two stores launched only a few months apart, but Apple had a significant head start in iPhone sales, so it's possible Android will keep catching up, especially since the (then) Android Market hit 10 billion downloads only last December.