xsnow is a program that runs on Linux. You can download it here (Windows and MAC versions are also available on this page at the bottom)
The snow falls and Santa and his reindeer fly across your screen. It runs on my desktop computer every year for the month of December. It really puts me in the holiday mood (you can see one of my screens below)
video of someone running it on their screen found here: https://www.youtube.com/watch?v=P4sPN_OTV1s
