An open-source alternative to the Play Store
F-Droid is an app store for Android devices. It's an alternative to Google Play that's characterized by the fact that it doesn't require a user account to download applications. Their apps are also open source and come with the source code so that developers can customize them to their liking. While the number of apps available on F-Droid is not as high as in Google Play, the selection is very good and offers a variety of tools.