Well, there are few programs for the PSX version simply because most PC programmers have the PC version (though I guess we could all get the PSX version too), but, more importantly, if we edit a file in the PC version we just save it onto our hard drive. If we want to edit a PSX file we ... uhh ... can't. Unless you burn a new CD ... and doing that every time you tested out a change would be very slow and expensive...
I think you can get a save game editor for FF7 PSX but I don't have a link handy. (Qhimm's Jenova can't edit PSX files ... can it?)
(Warning: next section contains extreme plugs for my own programs).
On the PC side of things:
Qhimm (you must have checked his site out to be here!) has
-a PC save game editor,
-an LGP extractor (extract files from the game archives)
-an audio player (play sound effects)
-and a background viewer (view the background graphics for field locations).
I (http://www.legacy-ovwp.org/~ficedula/index.html) have:
-an LGP extractor and editor (change the files too)
-a music patch (replace the midis in the game with any other format, eg. mp3's)
-a game editor (Cosmo), edit text, audio, and hopefully backgrounds soon
My game editors are based mostly off Qhimm's code so he's the real master here 
