ReactOS: NT4-compatible Open Source OS

It's definitely not cooked yet, but the folks working on ReactOS have released version 0.1.1 of the Open Source operating system aimed at creating a "stable and open" platform that is compatible with Windows NT 4.

This is an OS, not the windowing system, although the front page indicates that the developers are working with the WINE project, which is developing a windowing system API that is compatible with Microsoft Windows and runs in X-windows environments.