Falling more in the realm of desktop toy than traditional game is Flock [Itch.io link] by Murray Campbell, but it's something I've had running this morning and it's generated a low visual hum of contentment from my second monitor when I switch back to it between emails.
It starts as a bloom of tiny planes, emanating from a central point and leaving trails as they bounce between the sides of the screen.
The animatyion stops running when I focus on another application so I've been trying to stop it on a nice still image, leaving it as a transient screenshot until I go back and find another.
The red and blue colourway is my favourite as it seems the best for highlighting flourishes as the planes turn. That's the one in the header image. I'm not sure if there's a way to create custom colours - that would make my day. A fleshy rich coral background and flashes of teal as contrails in a kind of homage to Delacroix.
Flock is pay what you like on Itch.io