This is the cutest desktop widget I have ever seen. It's called MyFelix. You can download and install it, then it will appear on your desktop, eager to interact with you. I absolutely love it.

You can ask Felix to do various things - play with you, chase the mouse, catch a butterfly and so on. You can even pick him up to hold him. When you pet him, he will roll over and start purring like a motor. When you are done playing with Felix, you can put him back to sleep. If he is hungry, you can feed him. It is the cutest virtual cat I have ever adopted. You can download it here.