ReactOS
From OS-Tan Collections Wiki
ReactOS is a free(/libre/opensource) replacement for Windows. The project uses its own kernel and the WINE project for user-level tasks. It's OS-tan reminds a bit of Windows 2k, but she has GNU-horns and wears a lab coat with her symbol on it. As a pun on her name, she can be seen with a geiger-counter and a calculator. She is in a dliemma because on the one hand, she wants to be like the Windows-girls, but on the other one, she is disgusted by everything they stand for. She sees her studies as a refuge from these moral dilemmas.
See also: