Here's a great idea for small spaces-- movable walls!
Just think of the possibilities! Even if you have an actual house instead of a little apartment, a moving wall could make a room so much more useful! I am imagining:
~A craft room with movable walls-- move a wall to put away the sewing and pull one out to start paper crafting. All storage is built in, with pull down desks and fold-out inspiration boards, little drawers for little thing and large shelves for large things. and even built-in lights where they are needed.
~A toy wall in a child's bedroom. A Lego wall, a dollhouse wall, an art wall, etc. When it is time for clean up you can say "Alright, children, put your walls away."
~Two library walls, facing each other. If you want a book, pull them apart, and there you have a little library room all neat and tidy, and the books won't get dusty. Maybe there is a fold-down bench with cushions built in, too.
~What about an extra baking center wall in the kitchen? What looks like a breakfast nook could actually be extra kitchen work spaces in disguise. What about a wall to permanently house all the counter-hogging appliances?