This is different from O2Jam 3.5 which is Malaysian version.
O2Jam Malaysian/Filipino version uses Web launcher to login and looks in the regedit for patches and game installation
While O2Jam china doesn't require any registry entry and using ingame login screen.
This version is mainly used for Private Servers such as O2Jam V3 and O2ANGEL.
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In O2Jam you will find a variety of compositions ranging from soft ballads to heavy metal. It also gives players an opportunity to experience music composed by professional musicians. These are among the things that distinguish O2Jam from other music games. It is truly unique in every sense.

You have a sort of keyboard which is controlled by 7 keys on your keyboard. You have to play along with music. You will see notes falling in a bar on the left side and you see your character which you have to dress (by clothes and instruments and other stuff with gold coins you earn in the game)