IMVU is a free social website hosting a virtual chat room. It is operated by IMVU Inc and has been online for a long time. It has an active community of more than 3 million users from more than 90 countries.
The game itself is basically an Instant Messenger chat program using Virtual Persons as avatars for the players. In the beginning you get some virtual money to spend, which you can use to dress up your avatar and furnish your room. If you want to chat with someone, you can invite your friends or just ask for a random person. Emotes such as kissing, dancing, hugging and so on are available to use, along with some interaction with the environment you and your chat partner are in. You are also able to customize your homepage, setting up different public or private rooms and user groups similar to forums.
IMVU users are able to create custom content for the game, which they can sell for in-game virtual money after being reviewed by other IMVU users for catalogue additions.
The only real limitation in this "game" is customization; virtual money is given to you at registration, afterwards it can only be bought with real money.