WinRT is the Windows Runtime, and it forms the basis of Universal Windows Platform (UWP) applications. It can also be used for things like drivers, which lends itself to high-performance, native code. Microsoft mostly supports this use case with C++/WinRT, but they have recently announced that Rust will be joining C++ with Rust/WinRT.
The news is that Rust/WinRT now has a GitHub public preview.
Note that the Windows Runtime cannot be used for everything. For example, WinRT does not support Windows Presentation Foundation (WPF) and Windows Forms applications. As far as I can tell, OpenGL and Vulkan are also not available for WinRT. This is another cycle of the “push users to Windows Store” strategy that continually runs itself into a wall.
The adoption of Rust is still interesting, though. It is another big name that acknowledges the benefits of Rust as a systems language. Mozilla intended it to be used in web browsers, but all that requires is fast and safe. Lots of things need to be fast and safe.
Rust/WinRT is available on Microsoft’s GitHub under an MIT license.