This is a special Halloween-themed version of Skinnable Calculator, which you can download from the Play Store. The app is based on the open source project and is compatible with most Android devices. The theme includes a set of special icons, wallpapers, and fonts to give the user a different look and feel. You can also apply different themes to the app.

To apply the theme, first, you need to open the app and click on the (Apply) option. You will be presented with a list of themes that you can choose from. Next, you need to click on the theme you want to apply. You will be presented with a screen that asks you to make changes to the app. If you want to change the theme, you need to click on the (Change) option. You will be presented with a new screen, where you can change the color of the icons, fonts, and backgrounds. You will also be able to change the icons, fonts, and backgrounds of the app.