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What is a good Windows-compatible open source operating system?

I need an OS that can run Windows binaries, but I do not know many open source ones out there. I am not looking for Windows itself, but rather an OS that can run Windows binaries. Running Wine on Linux doesn't quite work with every program I am attempting to install. Since I have tried this, please don't suggest using Linux to run Windows programs.

Public Comments

1. XP or Vista
2. I'm not sure there is an open source OS that can run Windows software. It would be in breach of the WIndows license if it could wouldn't it? I assume you have looked into Linux?
3. Have a look at ReactOS http://www.reactos.org/en/index.html