Ragnarok Online.
Australia Server: http://www.ragnarok.com.au/ (Currently Free/Beta)
USA/International Server: http://iro.ragnarokonline.com/ (Pay)
South Korea Server: http://www.ragnarok.co.kr/ (Pay)
Japan Server: http://www.ragnarokonline.jp/ (Pay)
Great Britain/Europe Server: http://www.euro-ro.net/ (Beta)
Various Asia Servers: http://ragnarokonline.com/
MMORPG (Massive Multiplayer Online Role-playing Game).
Gets deathly addictive once you get the hang of playing the game. It's a bit like your Final Fantasies or your Zeldas where you would have to fight creatures & level yourself up - except there are also other players participating.
If you want to play/try out this great game go to the Australian Ragnarok website (link is mentioned above); register up your account, download the game installation file (650mb), and have fun!
The International (USA) server used to be free to play. Now it's "pay-to-play". The price is $17 AUD to play for one month. But there are other deals there to play 3 months, 6 months, yearly, etc.