Stars Without Number: Core.
Besides, the damn book is cool no matter how you look at it.
You can get it with either of the two covers - Star Field like the original free version of SWN of the Alien cover that has been seen previously on the SW: Core PDF.
I am not sure if the Star Field version comes with a free copy of the SWN: Core PDF, as it is linked from and packaged with the SWN Free Edition. In any case, I went with the Alien Cover myself ;)
(just realized that the Hard Cover version is only available with the Star Field cover. Ah well, I wanted Soft Cover anyway)