You might be aware of the open source. F-Droid consists of all of the apps that are available as open-source. Here you can download the apps that are not available on Google Play Store. You can find some of the apps listed in this article on F-Droid.
This app doesn’t consist any pirated or cracked software. You might have heard about an app named “Black Market.” This app is nothing like that. This app is great for exploring the new open-source apps that you can’t find on Google Play Store.