Most doors are boring, this one -- by Tobias -- is not. At first glance, it looks like a standard door, but push the center portion down, and it becomes a ping pong table. No word yet on if this concept will go into production. Click here for one more picture.
The only requirements are the adjacent rooms have enough room for you to play in. The only downside is one side of the door looks normal while the other is bright green. Try fitting that into your home decor[via YankoDesign]