No don't be alarmed Windows OS is not getting open sourced. Windows 10 free upgrade was stopped this month two years ago.
What I want to discussed today is ReactOS, it is a free and open-source operating system intended to be binary-compatible with Windows operating system. What it means is you can run any windows application on ReactOS effortlessly.
Initially it was started as a clone of Windows95. Most of the development was done in C/C++. It is still in alpha. The latest version 0.4.8 can be downloaded from there website.
The following video can help you start right away.