Flooring a concrete deck, without raising the floor (much)
Rubber tile or mat would be one simple approach - see duckboards for another method/approach in polymers or sometimes treated wood.

Given a solid, correctly sloped concrete substrate, pressure-treated 2x4 sleepers and a deck with no posts, etc. should work just fine - the 2x4's can even be laid flat, since the concrete deck is taking the load directly.

Paint on or pour on rubber (acrylic/polyurethane, possibly with rubber granules) coatings as for pool decks or perhaps tennis courts might also work, and might cost less.