Roblox

Designed to appeal mainly to kids 4-14, Roblox is a family friendly sandbox MMO. Players can create their building-block avatar, explore the virtual world and interact socially, construct many different types of buildings as well as create games of their own with the built-in accessible tools. Once approved, these user-generated games are available for multiplayer participation via the game's client or website. When other players visit their creations, users earn in-game currency, which can be exchanged for clothes and building materials.