Everyone knows about Line Rider, right?
Well, if you don't, here's a brief description of this free to play experience.
Using the mouse, players draw lines to create a course on screen. Once they are happy with their design, simply press play and watch as a young lad on a sledge tackles the player made creation.
Everyone usually starts with a simply diagonal line, but members of the Line Rider community have come up with some amazing course designs, which must have taken them hours.
If you want to give it a try, you can play Line Rider here:
Here's my favourite Line Rider video. This shows what can be done with a little patience: