Screen Mates (often called Desktop Pets) are a category of software most popular in the early to mid 2000s, bringing more to the idea of an interactable desktop on your computer. Many popular Screen Mates were marketting efforts or advertising from different brands (E.x. My Felix by Purina), but there were many developed independantly too.
These mates were usually very simple, consisting of some type of pet that would wander around your screen or pop up every so often. Some had additional features, such as the need to eat and sleep. Not all Screen Mates were restricted to the desktop either, as many were developed as screen-savers.
Over time, the desire or enjoyment from Screen Mates died down and overall development around them slowed to a halt. Many of the older Screen Mates are still up, but some are no longer functional due to their requirements of a viable server.