ReactOS is a complete rewrite of the Windows (Windows NT) kernel. As such, it is intended to provide a complete operating system replacement for Microsoft Windows, that is compatible with all Windows applications and drivers.
The project grew out of the FreeWin95 effort to clone Windows95, but was renamed ReactOS when work was re-started from scratch building a clone of the Windows NT line that includes NT, Windows Server 2003, Windows XP, and Vista.