Windows Core OS
Windows Core OS (abbreviated as WCOS) is an internal Microsoft effort that aims to provide a universal, modular base for future versions of Microsoft Windows. The operating system is still based on the NT kernel, although most legacy features found in regular desktop Windows have been stripped out. Instead of the traditional Windows Explorer shell, the platform uses a newly built GUI stack based on DirectX and the UWP/WinUI frameworks. By default, WCOS variants are not natively compatible with applications using the legacy User and GDI libraries for their user interface, however, they can run virtualized using either remoting or a purpose-built container.
The introduction of a common core for all Windows-based products has been planned back as early as 2002. However, actual work didn't start until 2014 with OneCore, which unified all products previously using separate forks of the Windows codebase into a single source code repository, enabling everything to be built from a single codebase although each product still provided its own shell on top of the common core. Windows Core OS is a natural extension of this effort, as it provides a common modular shell which can be customized for individual needs of each product.