The Endless Forest by Tale of Tales is an MMO with a difference; it’s a screensaver. You play a deer, identifiable only by a unique symbol over its head. Certain actions will change the appearance or voice of your deer avatar, but otherwise there is little to achieve while playing. It is a game without opportunity for violence, without goals and without pressure.
Strangely, with very limited options for communicating with or identifying other players, I have found I play much more sociably than I do in regular MMOs where I can be identified by name. I particularly enjoy the music that plays when you dance and is built upon when you dance with others.