With the addition of a shelf, the space over a door becomes a useful and almost hidden place to store things:
Use it in a bathroom to store extra towels, toilet paper, perhaps even a box of medicines and first aid supplies (keeping them out of the reach of small children yet close enough at hand that you may be able to declutter your medicine chest of things you don't use daily!);
In the kitchen, it's a great spot for little used cookbooks and pots;
In the bedroom, it can hold extra blankets and the extra linens for each room.
Check out this easy tutorial from Home Depot so you can install one yourself this weekend!
Image: Home Depot