reactos

Guess what does the following screenshot show?

No it is not Windows. It does look and feel like Windows, but this baby is Free Software, an operating system called React OS.

Why does it look like Windows? Because React OS is a project of developing a Microsoft Windows compatible operating system. It is supposed to run programs and even drivers meant for Windows and it is supposed to look like Windows so that former Windows users can ease right into it without feeling that scary feeling: the difference.