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.