Last one to hit the wall is a rotten egg!
Stairslide: A Modular Slide System For Kids To Ride Down The Stairs

This is the Kickstarter campaign for the very cleverly named Stairslide, modular plastic slide pieces that can be nested on top of each other to create a slide to fit any length stairs. Each piece covers three stairs, so divide your total stairs by 3 to figure out how many pieces you’ll need. For reference, a 3-piece set for nine stairs is approximately $100. For further reference, when I was a kid we used to just ride down the stairs on a big pillow. Or, if we really wanted to risk injury when we hit the front door, a laundry basket or baking sheet. *unconsciously rubbing plate in neck* Those were simpler times.

Keep going for their Kickstarter video.