Yes! – it’s real, it does exist:

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with every purchase of Rhino3d you get also the Rhino OSX  version.  it is a “beta” version (still in development), but already very usable, and used by many Rhino users worldwide in production.

the rhino 4 .3dm format saved by the OSX beta is compatible wit ( for rhino 5 betas you need te rhino.i for rhino v5, you can get this too if you need for v5 format)

as option,  the Rhino windows versions runs perfect smooth  in  virtual OS environments like parallels desktop or vmware, if you prefer that: