A program by Sony that acts as an interface for email. It's a cross between Eudora, Tamagotchi, Sanrio's Hello Kitty, Microsoft Bob, and a fluffy pink version of the ILOVEYOU script.
It's designed to make email more fun and easy for novices that can't/won't understand the concept of electronic mail.
The way it works is this:
You write an email to a friend (who also uses PostPet), and your pet (often a large pink teddy bear in the advertisements) goes to your friend's pet's house to deliver it. There, your pet can make friends (or enemies) with the other pet, your friend can slap your pet silly or pat it, your pet can run away from home, your pet can learn "weird dances," and so on.
One of the best things about PostPet is that your pets can die from abuse or malnutrition and they cannot be resurrected, thereby ending your ability to ever use PostPet (on that computer).
There's also the members only PostPetPark, where users can download new plugins to add new actions, snacks, illnesses, and interiors and accessories for your pet's small 3D room, as well as participate in intellectual discourse between users about issues their pets may have.
This program is insanely popular in it's home country of Japan (home of Tamagotchi-related vehicular homicide), winning the 1997 "Multimedia Grand Prix" award from the Minister of International Trade and Industry. It's now available in several languages, including English.
Characters in the PostPet world include:
(These are their real name
I don't know whether to laugh or cry when I see this thing. It's interesting, in that embarrassing consumerist Japanese culture way, but at the same time, it scares the hell out of me because people actually think it's useful.