If you're a close follower of Windows and Microsoft, you might remember the rumors of an operating system known as Polaris. It was believed to be a streamlined flavor of Windows Core OS for new PCs, cutting out legacy features in favor of better battery life, and performance on lower-end hardware. It was eventually canceled in favor of Windows 10X, but an early build of Polaris recently leaked online, confirming the project was actually once a thing at Microsoft (via Windows Central.)
Interestingly enough, this early Polaris build is designed for ARM32 PCs, like the Surface RT. However, it's not really something to install, as there's no Windows Shell, and there are no apps in the release. Zac Bowden reports that the leak is an RS3 RTM build, confirming that Microsoft has been working on the project since at least 2017. Again, though, there isn't anything new or anything most people can play with in this leaked build. It's rather designed for professionals who are interested in tweaking and exploring an unreleased version of Windows.
While there isn't much to this leaked build, it's still something you might want to check out. We don't endorse or recommend installing it, but it's available dow download on the Internet Archive.