I found this plant invading an unirrigated school yard lawn in Everett, Washington (USDA zone 8a):
This plant is very effectively competing with the grass and might make a good lawn replacement. The foliage is feathery similar to many plants in the Asteraceae family. It spreads on rooting stolons as seen below.
Does anyone know what it is? Since it has been regularly mowed, I do not know its mature height or anything about its flower. My best guess at the moment is some sort of yarrow (Achillea).
The plant is on my way to and from work. So if you need me to verify any identifying features, I can do that.
The foliage of this plant is not especially aromatic. If I smash up a bunch of leaves and stuff them in my nose (and close my eyes and think of Kentucky), they smell slightly grassy.