stands for Good Game, Peace Out and it is an online matchmaking system for fighting games.

it still is in alpha stage of development and the idea behind it is to provide a very good netcode that will prevent the games of having input lag which is crucial to fighting games.

somehow the netcode is outstanding and has some great magical algorithms implemented.. you can play from Europe with American players and have a good responsive game. (Kaillera or other similar systems have nothing on this)

currently, in this development stage, there are two games supported:
Street Fighter Alpha 2 and Marvel vs Capcom. devs opted for only one game at the moment in order to iron out all the bugs within the GGPO Client before implementing more games.

to get things going follow the few easy steps in this Installation Guide.
you'll need to Signup first into the online system.
you will need of course the SFA2 rom, of which you should ask Google ;)

the GGPO Client has a game lobby and a worldmap on which players are pinpointed according to their IP (usually in the form of city and country).

there are few players from Europe at the moment which i try to change right now, but i predict a big revival of fighting games once the system will be polished.. this year should boom with activity if all goes well, especially with new features like ranking, spectating etc. :)

all of this having been said, Good Game & Peace Out :D

PS: i'm looking forward on playing ESR members, making some sort of weekend minicups wouldn't hurt either -> discuss :)

PS2: thanks to tzz for discovering this