Calculator (Holo) is a comprehensive open-source calculator app developed by Xlythe Calculator that offers a range of advanced math functions. The app is available on Android 9.0 and is free to use.

The app has a user-friendly interface that displays only the basic functions when opened. However, by swiping left and right, users can access different branches of math. The app includes features such as history, graphing, hex/bin conversion, matrices, and more. While the app doesn't solve equations for you, it provides users with the tools to do so themselves as conveniently as possible.

One of the unique aspects of Calculator (Holo) is that it is completely open source, which means users can access and modify the code if they want. The app comes bundled with some phones, making it a popular choice for users who need a reliable calculator app that is easy to use and customize.