Some apps exist on thousands of phones. Others live on millions. Only a few occupy hundreds of millions. Google Photos, HP Print Service Plugin, and Android System Webview are the latest apps to surpass 500 million installs.

If you've purchased an Android phone recently, you may have noticed that each of these are apps that come pre-installed. That takes some of the wind out the sails of this news. When a pre-installed Google app reaches this milestone, it's not quite as impressive as when an app manages this feat via Play Store downloads. Facebook's apps -- Instagram, Messenger, and the main Facebook app -- sometimes come pre-installed, but many users undoubtedly seek them out when they don't.

Google Photos launched during last year's Google I/O. Android System Webview hit the Play Store a few months earlier. The HP Print Service plugin, aside from being the least interesting, debuted in 2013. Some pre-installed apps take longer to hit half a billion than others.

Google Photos
Google Photos
Developer: Google LLC
Price: Free

Android System WebView
Android System WebView
Developer: Google LLC
Price: Free

HP Print Service Plugin
HP Print Service Plugin
Developer: HP Inc.
Price: Free