"ReactOS is an open source (GPL) operating system built to be
compatible with Windows NT applications and drivers. ReactOS is
currently just a development platform; it is not a useful desktop
system for the average user in any way, but it has potential.
"The makers of ReactOS work closely with the WINE project,
sharing as much of the programming effort as possible. While they
now concentrate on Windows NT, future releases are planned to offer
compatibility with Windows 2000 and XP..."