This lovely thing is Sagina subulata aurea - Golden Irish Moss. I think it is much prettier than the plain old green version. It is a low growing ground cover that will grow in some sun to quite a bit of shade. I don't think full sun would make it happy. It is the kind of plant you can get growing between stones on a walk and it will take light foot traffic, though I always feel a bit uncomfortable walking on any of my plants. If you do use it between stones, be sure there is enough space for it to grow, because it will spread. I even have it growing on top of rocks, so my guess is that super fertile soil isn't one of its requirements. It has tiny, dainty white flowers in the spring which look kind of like you just took a handful of these super miniature blooms and just threw them across the ground. Quite a nice effect. It is relatively easy to transplant as long as you keep it well watered for a few weeks after you transplant it. You won't find a huge root system, so a bit of babying is necessary to a successful transplant. This golden form is not as easy to find as the green one, but so much prettier.