Penny Floor - don't know if I would have the patience for a whole floor. but a coffee or patio table would be nice! Also an easier way to do it is to put out the pennies then flatten then by, I don't know, maybe a broom or some thing.
Simple built-in to create a mudroom and/or storage anywhere from an entry, to kids room or in a laundry room by adding shelves or a deeper bench for sitting. Put drawers under bench or have the seat lift up to store things.