In the world of massively multiplayer online games (MMOGs), Faunasphere was but a blip on the screen in its short public life from 2009 to 2011. Its devoted players, many of them middle-aged women, entered a world that did not build on common fantasy or science-fiction tropes. There was no evil to defeat or realms to conquer, only friendly animals to care for and pollution to fight.

In Players and Their Pets, Mia Consalvo and Jason Begy argue that its very difference makes it critically important--even more so than the large, commercially successful games such as...