[Kamrom]

1.Super Famicom Hard
2. Super Famicom Easy
3. SNES
4. PSX of Hard type
5. Wonderswan color
6. Port of wonderswan color to GBA
7. The After Years, FF4's sequal, on Mobile and Wii
8. DS Remake
9. PSP "Final Fantasy 4 Complete" which has the original game, After Years, and a third NEW game between them called Interlude (for some reason.)

I own 3,4,6,7,8 and 9. Like right now i can play them, any of them. Currently, I had a game in the bugged GBA version, while slowly earning up in the new DS remake, and starting up the After Years in my copy of Complete.

They have virtually none of the same features:

FF2 SNES was mostly a mix of hard and easy type. It removed special abilities (like dark wave) and replaced the egrab bag status items with "Remedy". That sorta thing.
The PSX was basically FF4 Hard Type translated, but its atrocious loading time made it unplayable.
The GBA port has a bug that skips over people due to a quirk with the ATB system. You can exploit it with enemies just by spamming Attacks and they'll never get a turn (The trap doors dont even get Target out.) It also has a spiffy new dungeon or two. And you even get to swap characters! In addition you have the usual superboss.

The DS port was a whole new game. And its like a Final Fantasy game made by enix, since...thats what it is. The game increases in huge stupid bursts so a single Surprised encouner with an Area magic attack will usually kill you before you can react. You also have wholly redesigned and new abilities, a very interesting game at the very least. You can even battle Whyt, an Eidolon, with other people online.
You cannot, however, switch party members. Nor is there the same extra dungeon. Namingway is now a bunny and insane. (voice acting...Remember FFX? Its either that or never hearing your characters name out loud.) Also has a bizarre new Augment system to give characters other characters powers. It also has a superboss, but not the same superboss as GBA.

The PSP version has FF4, After years, and its new Interlude sequal. It uses a 2D center design, wholly redone in the original style, much more faithful that the DS one. This same engine spans all three games on the disc, and all were made together so it looks really spiffy.
It does not however, have voice acting, augments, extra lunar ruins dungeon, party swapping.

Sooner or later im actually gonna finish one. They just have to stop releasing new versions before i can.