I have a small condo, carpet covered, that will soon need to be replaced. Bailey runs to that and scratches whenever she's excited. It's a round tube for a base, with a hole cut out, but she never goes inside. It has a platform on top that she sits on, but mostly she loves to scratch it.
They also use their turboscratcher - which lies on the floor, and is cardboard.
Bailey loves scratching big cardboard boxes that are full of heavy stuff, so they don't move.
They ignore their sisal scratching post, I think because it's not very solid, and tips when they stretch up to grab it.
Bailey also loves a new thing I bought - it's an s shape, carpeted, with one hump of the S covered in sisal matting. It sits on the floor with one hump in the air, sort of, so one concave section, and one convex. She loves it, she plays with it, hides under the hump, snuggles into the concave bit, and sleeps draped over it. And scratches it, a lot.