This game is now defunct, but I figured it deserved a thread to honor it!
"Zone 4: Fighting District was a free-to-play brawler MMORPG. Players were able to choose from six characters and several fighting styles, each of which contained hundreds of special moves. Zone 4 includeded a persistent central hub, competitive PvP modes, and a cooperative story mode wherein up to four players could work together to clear instanced stages. Zone 4 has the same Arcade brawler feel as Dungeon Fighter Online, but boasts 3D graphics and ditches the fantasy theme in favor of a modern feel.
Fighting Styles – Tae Kwon Do, Muay Thai, Boxing, Capoeira, Pro Wrestling, Judo, Hapkido, Sambo, Kung Fu, and many more!"
The best way I can describe it is, imagine if Powerstone 1 was an MMO. It was incredibly fun, could be quite competitive and tense at times. There was no pay-to-win, at least in PvP, and the skill ceiling was decent.
I know this is weird, but I figured maybe someone else remembers this game?