Mow

Move across the lawn to mow it. It grows back from the edges. Leave a patch alone long enough and it might flower.

There's no goal. I made this after a long evening of thinking about a grass-cutting game where everything has a goal, and I wanted one where nothing does. Grass doesn't appear from nothing here; it only creeps in from neighbours that are already growing, which is why your paths heal from their edges inward.