For the uninformed, the Final Fantasy Box Set (FFVII, FFVIII, FFIX): Official Game Guide comes with redesigned strategy guides with new high-resolution screenshots for Final Fantasy VII, Final Fantasy VIII and Final Fantasy IX. Also included in the package are three holographic prints, one for each game, that are secured via a magnetic slip case. Unfortunately, we do not currently know how these extras look like.
Final Fantasy VII first came out for the PSOne before being ported to the PC. It was eventually re-released for the PlayStation 3, PSP and Vita as a digital download as well. Moreover, Square Enix announced at PlayStation Experience that the updated PC version will be ported over to the PlayStation 4 next spring.
Final Fantasy VIII also came out for the PSOne, PlayStation 3, PSP and Vita along with getting an updated PC port. On the other hand, Final Fantasy IX stayed exclusive to the PlayStation platforms.