Any fun online multiplayer games that dont need downloading?

My brother plays games "like" runescape. It's the runescape world and the graphics and your avatar is the same, but you level up quicker, and pking is different. There are only the good weapons and armour. It's easy to make money on it and you can get anything you need in like a couple hours. They're called private servers. I dunno if your interested but if you are you can email me.