Microsoft has open-sourced their Windows 10 Calculator so that anyone can play with it. The full source code for the Windows Calculator is now available to anyone who wants to give it a download and try compiling it. Users will need to be running Windows 10, version 1803 or newer and install the latest version of Visual Studio. Microsoft also feels that this project can provide a good introduction into various Microsoft technologies such as Fluent app design, the Universal Windows Platform, Azure Pipelines, and more. Developers can also submit bug reports, help fix bugs, and extend the functionality according to these guidelines.
Source: https://www.bleepingcomputer.com/news/microsoft/microsoft-open-sources-the-windows-10-calculator-on-github/