Raining Squares by Sebastian Mihai is a Sega Dreamcast VMU homebrew tech demo. The VMU is also sometimes called VMS. The background is animated, the player controls a pixel, moving it left right, and there are falling squares which appear at random X positions, and have random sizes. There is a delay every time the player’s pixel collides with a falling square.

http://sebastianmihai.com/main.php?t=123&n=Sega-Dreamcast-VMU-development-Raining-Squares