>> plan9/inferno, qnx, например :3. еще вроде aix, но я с ним дела не имел
> Вот вы ими и пользуйтесь наздоровье, а я пешком постою и пингвином
> попользуюсь как-нибудь. Он может и не расово верный с точки зрения
> академиков, зато работает и довольно хорошо.
> p.s.: не очень понятно почему вы мне отвечаете, а не тому индивиду.

Вы невкуриваете, UNIX - это:

From February 1995, computer systems have carried the UNIX brand if:

They guarantee to support the services specified in the Single UNIX Specification.

Customers can identify UNIX certified products by the Open Brand logo and the mandatory
attribution declaring to which version of the specification the product complies:

- UNIX 93 applies to UNIX system products which pre-date the Single UNIX Specification.
- UNIX 95 applies to UNIX system products which conform to the Single UNIX Specification.
- UNIX 98 applies to UNIX system products which conform to the Single UNIX Specification , Version 2.
- UNIX 03 applies to UNIX system products which conform to the Single UNIX Specification , Version 3.

See the platform pages for the latest information.

In licensing the UNIX brand a vendor warrants and represents that every certified product:

    - Conforms to the specification.
    - Meets The Open Group's test and certification requirements.
    - Will continue to conform to the specification.
    - Will be rectified within an agreed time should it be found to be non-conformant.

UNIX certification is widely recognized as the international symbol of assurance in open systems.
By the end of 2001, the value of procurements of open systems referencing the brand had exceeded $25 billion.

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Из того что вспомню - в Linux нету <float.h> и <iso646.h>

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Кстати, самый "чистый" UNIX живущий до сих пор - SCO OpenServer :)