It's another desktop pet, just like what Ukagakas are! Except this is not quite as free, because you don't make it from scratch, instead there's a base, and you can replace animations and things with other stuff, but it is still limited to a set amount of animations.
It's easier to set up and run though, because it's both on Git, and on Steam. It even has workshop support! (to be fair most of the mods are in Chinese unsurprisingly) Also has a ModMaker, though making a full avatar replacement is a huge undertaking as there's a few hundred animations to replace, so it's not something you see often.
Desktop pets are these cool little things that run around on your screen, they can be forced being on the desktop or on top of windows if that is what you want.
They can be more like actual pets you have to take care of, VPet falls more into this category, or they can just be something that exists, says things, or does some useful things. From what I've noticed Ukagaka fall into this category. There's been a new trend with stuff like Desktop Mate or MateEngine (if you want to check these out, I recommend MateEngine more, as it's free if you get it from Github and it's not as scummy), but honestly I think these are the worst of all, they might be 3D, but they aren't really capable of doing anything, and just exist to exist.