With virtual Petz, both cats and dogs, from PF Magic, users can invite autonomous agents to play on their desktop. A user might interact with her Petz by petting them, by introducing them to one another at different ages, by feeding (or not feeding) them, and so forth. Unlike with Creatures, users do NOT have direct access to any sort of slider-bar tweaking of internals. In this way, a user's Petz are truly autonomous. The Petz agents use real-time animation, and the layering display of multiple simultaneous behaviors, to create the illusion of lifelike continuous motion.
Petz graphical behaviors mimic those simple behaviors we expect of real pets: Dogz, for example, wag their tails, have perky ears, expressive eyes, have noses that follow ``scents'', have spots in which they like to be petted, and have tongues that can be used to express being tired, excited, thirsty, and hungry.
Petz have persistent personalities, but these can change over time if, for example, a pet is not fed appropriately (pets come with virtual food, and virtual toys). Additionally, users can modify the behavior of their Petz by squirting them with a virtual spray bottle.
Like the NPCs in Ultima Online (see below) the newest version of the product allows Petz to interact with one another. Some relationships are biased (e.g., dogz and catz will tend not to get along well, older Petz nurture younger Petz), but these too can be indirectly affected by the user.
From an agent-sociological perspective it will likely be interesting to study the nature of the long-term relationships that develop between users and their Petz, and the virtual communities that have sprung up on the web for discussing and sharing information on Petz.