I have been working on some retro themed live wallpaper which you can download free from here:
https://www.opencode.net/pentad/livewallpaper
The images are in GIF format and should work on Windows, Mac, and Linux. I'm using Linux and had to get a free program that allows animated gifs as wallpaper.
You will find:
Atari
CBM
Tandy
Mac
IBM
and others.
The Atari Swan animation from the 800 caused many of my colleagues to ask about Atari and the demo.
I also have some free retro themes for Linux here:
https://store.kde.org/u/pentad
If you are using the SDDM greeter you can get Atari themed login displays. I thought the ST one came well.