This is Microsoft's open-source Windows Calculator, the production calculator app shipped on Windows. The repository is a full UWP/XAML application with Standard, Scientific, Programmer, Date, Unit Converter, and Graphing modes. The core is split into `CalcManager` (a native C++ calculation engine implementing arbitrary-precision rational arithmetic via the Ratpack library), `CalcViewModel` (C++/CX view models handling history, memory, copy/paste, unit data, navigation, and state snapshots), `Calculator` (the C#/XAML UI shell), and `GraphControl` (a DirectX-based graphing control). The app is MVVM-structured, heavily localized in 25+ languages, and includes both C++ unit tests and WinAppDriver-based UI tests.