Virtual world games include "Club Penguin," "Twinity," "Second Life" and "Onverse." Each game allows players to create an account free of charge, as of July 2015.
Disney created "Club Penguin," a virtual world designed for children. Players can customize penguins, play games, adopt pets and chat with other players.
"Twinity" focuses on realism, with realistic avatars and geography that's based on the real world. Players create avatars and can then go to parties, shop and chat.
"Second Life" is designed to mimic the real world. After creating an avatar, a player can interact with others, create art and build new parts of the world.
In "Onverse," players can play games, go shopping and customize both their avatars and apartments.