If you want to run a clone of Microsoft Windows to escape the drama of upgrading to Windows 10, try ReactOS -- but do not expect it to be a fully functional replacement. ReactOS is a free, open source operating system built on the design principles found in Windows NT. ReactOS is a Windows clone and not a Linux distro. However, the release last month of version 0.4.1 brings this unique open source project one step closer to its goal of providing users full compatibility with Windows software on a free OS made almost from scratch.