boxfit(6x) on Linux
The text 7d59815064ad, as Debian 10 (Buster) shipped it.
fills space with a gradient of growing boxes or circles.
Flags it lists
-
-border -
-circles -
-count -
-delay -
-fps -
-grab -
-growby -
-peek -
-random -
-root -
-spacing -
-squares -
-visual -
-window