1) Is this some recent port? Did the original game in 2002 come out on PC too? Were there any other ports before?

There seem to be surprisingly little info regarding PC releases on Wikipedia and mobygames.

2) Is there a single player campaign or something? Or is it just like Mortal Kombat with single battles only?

The ROM file is in the files, so I'm assuming it's emulation and not an actual port. I believe it's one of the last Neo Geo releases. I don't know about the campaign or lack of, I haven't played it.

Edit: just played some of it, it's definitely emulated NeoGeo. If there's a story mode I don't see it, but having said that, it plays well once you work out the controls.

Mm.. not sure if this version is worthy even as a freebie..

There is no story in KOF 2002.

The old KOF is 3-games with story, then 1 break. Story of Kyo Kusanagi is told by KOF 95 96 97, and then 98 is the break.
Then they continue the story with new main protagonist "K" with KOF 99, 2000, 2001. KOF 2002 is the break.

I stopped playing after some korean company bought snk and they introduced a disgusting girly boy (was that even a boy?) to be the main protagonist for 2003

When you say Nebula, you mean this?
http://nebula.emulatronia.com/ I was more interested in whether there is a campaign, story or no. What's the game mode like?

Well, the story is told in arcade mode. Usually they give you cutscene after every 3 fights. But there should be none in "break" title. Can't remember. It's been a long time

Sorry, I wasn't clear. I'm not interested whether there is a story or not. What I'm interested in is if there is a campaign. What's the "arcade mode" you mentioned?

Pick your team and fight until last boss

It's literally the arcade game in a ROM, wrapped up with an emulator. There's a single player mode where you battle other teams until you reach a final boss.

If a second player joins, you fight each other.

Nothing more complex than that. Welcome to arcade fighting games. :)

Wow, you're so threatened by a fictional character's appearance and mannerisms to call him disgusting?

I mean I hate the character too, but because he's a dick. At least I hated him until XIII. Then it all made sense.

ZFR: Yes. DotEmu licensed the Nebula emulator from ElSemi (the author) and modified it to add the menus and such, but in the process, messed up the simple stuff like pad configurations. I downloaded the GOG version of the game and it works... okay, but man, their Steam versions other NeoGeo games (not the KOFs, I mean everything else) are pretty crappy.

The game data files can be copied and imported into another emulator, like Final Burn Alpha, which has more configuration options available.