I would say, use any Linux distro your comfortable with. Then pick a BSD, like netbsd, openbsd and so on...
Then you could install Solaris since its available on x86 platforms as well...
Not sure about a 4th though, maybe something like QNX or something like that.
1. Linux
2. BSD
3. Solaris
4. QNX or any other *nix OS that is x86 compatible.
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