Kicks Online is a free-to-play football MMO (Massively multi-player online) developed by emerging Korean designers Entermate. Since it's launch in July 2006, they claim it now has over 300,000 registered users, probably due to the fact that this is a highly playable game with great graphics and provides an interesting variation to normal football.
Kicks Online follows 'street football' rules with the appropriate tactics which involves different ways of passing the ball and various surfaces.
Whatsmore, the better a player plays, the more his character's skills improve. Matches can be played 3v3, 4v4 or 5v5 mode and can be played in highly unconventional settings such as roofs or even factories.
The graphics are outstanding considering this is a totally free game featuring cartoon style 3D scenes and characters. The only drawback is that there can be a serious lag when playing against online opponents although much of this will depend on your internet connection.